Fix scope of ReadOptions in SstFileReader

a4a4a2d changed the contract of `TableReader::NewIterator()` to require
`ReadOptions` outlive the returned iterator. But I didn't notice that
`SstFileReader` violates the new contract and needs to be adapted. The unit test
provided here exposes the problem when run under ASAN.

```
$ ./sst_file_reader_test --gtest_filter=SstFileReaderTest.ReadOptionsOutOfScope
Note: Google Test filter = SstFileReaderTest.ReadOptionsOutOfScope
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from SstFileReaderTest
[ RUN      ] SstFileReaderTest.ReadOptionsOutOfScope
=================================================================
==3238048==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7ffd6189e158 at pc 0x000001298350 bp 0x7ffd6189c280 sp 0x7ffd6189c278
READ of size 8 at 0x7ffd6189e158 thread T0
    #0 0x129834f in rocksdb::BlockBasedTableIterator::InitDataBlock() table/block_based/block_based_table_iterator.cc:236
    #1 0x12b01f7 in rocksdb::BlockBasedTableIterator::SeekImpl(rocksdb::Slice const*) table/block_based/block_based_table_iterator.cc:77
    #2 0x844d28 in rocksdb::IteratorWrapperBase<rocksdb::Slice>::SeekToFirst() table/iterator_wrapper.h:116
    facebook#3 0x844d28 in rocksdb::DBIter::SeekToFirst() db/db_iter.cc:1352
    facebook#4 0x52482b in rocksdb::SstFileReaderTest_ReadOptionsOutOfScope_Test::TestBody() table/sst_file_reader_test.cc:150
    facebook#5 0x5f433c in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3899
    facebook#6 0x5f433c in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3935
    facebook#7 0x5cc2de in testing::Test::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3973
    facebook#8 0x5cc988 in testing::Test::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3965
    facebook#9 0x5cc988 in testing::TestInfo::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4149
    facebook#10 0x5cce9a in testing::TestInfo::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4124
    facebook#11 0x5cce9a in testing::TestCase::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4267
    facebook#12 0x5ce696 in testing::TestCase::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4253
    facebook#13 0x5ce696 in testing::internal::UnitTestImpl::RunAllTests() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:6633
    facebook#14 0x5f541c in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3899
    facebook#15 0x5f541c in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3935
    facebook#16 0x5cee74 in testing::UnitTest::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:6242
    facebook#17 0x4c0332 in RUN_ALL_TESTS() third-party/gtest-1.8.1/fused-src/gtest/gtest.h:22104
    facebook#18 0x4c0332 in main table/sst_file_reader_test.cc:213
    facebook#19 0x7fb0263281a5 in __libc_start_main (/usr/local/fbcode/platform007/lib/libc.so.6+0x211a5)
    facebook#20 0x523e56  (/data/users/andrewkr/rocksdb/sst_file_reader_test+0x523e56)

Address 0x7ffd6189e158 is located in stack of thread T0 at offset 568 in frame
    #0 0x52428f in rocksdb::SstFileReaderTest_ReadOptionsOutOfScope_Test::TestBody() table/sst_file_reader_test.cc:131

  This frame has 9 object(s):
    [32, 40) 'reader'
    [96, 104) '<unknown>'
    [160, 168) '<unknown>'
    [224, 232) 'iter'
    [288, 304) 'gtest_ar'
    [352, 368) '<unknown>'
    [416, 440) 'keys'
    [480, 512) '<unknown>'
    [544, 680) 'ropts' <== Memory access at offset 568 is inside this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-use-after-scope table/block_based/block_based_table_iterator.cc:236 in rocksdb::BlockBasedTableIterator::InitDataBlock()
...
```

The fix is to use `ArenaWrappedDBIter` which has support for holding a
`ReadOptions` in an `Arena` whose lifetime is tied to the iterator.

Test Plan: verified the provided unit test no longer fails

table/sst_file_reader.cc

@@ -7,6 +7,7 @@
 
 #include "rocksdb/sst_file_reader.h"
 
+#include "db/arena_wrapped_db_iter.h"
 #include "db/db_iter.h"
 #include "db/dbformat.h"
 #include "env/composite_env_wrapper.h"
@@ -62,18 +63,23 @@ Status SstFileReader::Open(const std::string& file_path) {
   return s;
 }
 
-Iterator* SstFileReader::NewIterator(const ReadOptions& options) {
+Iterator* SstFileReader::NewIterator(const ReadOptions& roptions) {
   auto r = rep_.get();
-  auto sequence = options.snapshot != nullptr
-                      ? options.snapshot->GetSequenceNumber()
+  auto sequence = roptions.snapshot != nullptr
+                      ? roptions.snapshot->GetSequenceNumber()
                       : kMaxSequenceNumber;
+  ArenaWrappedDBIter* res = new ArenaWrappedDBIter();
+  res->Init(r->options.env, roptions, r->ioptions, r->moptions, sequence,
+            r->moptions.max_sequential_skip_in_iterations,
+            0 /* version_number */, nullptr /* read_callback */,
+            nullptr /* db_impl */, nullptr /* cfd */, false /* allow_blob */,
+            false /* allow_refresh */);
   auto internal_iter = r->table_reader->NewIterator(
-      options, r->moptions.prefix_extractor.get(), /*arena=*/nullptr,
-      /*skip_filters=*/false, TableReaderCaller::kSSTFileReader);
-  return NewDBIterator(r->options.env, options, r->ioptions, r->moptions,
-                       r->ioptions.user_comparator, internal_iter, sequence,
-                       r->moptions.max_sequential_skip_in_iterations,
-                       nullptr /* read_callback */);
+      res->GetReadOptions(), r->moptions.prefix_extractor.get(),
+      res->GetArena(), false /* skip_filters */,
+      TableReaderCaller::kSSTFileReader);
+  res->SetIterUnderDBIter(internal_iter);
+  return res;
 }
 
 std::shared_ptr<const TableProperties> SstFileReader::GetTableProperties()

table/sst_file_reader_test.cc

@@ -128,6 +128,31 @@ TEST_F(SstFileReaderTest, Uint64Comparator) {
   CreateFileAndCheck(keys);
 }
 
+TEST_F(SstFileReaderTest, ReadOptionsOutOfScope) {
+  // Repro a bug where the SstFileReader depended on its configured ReadOptions
+  // outliving it.
+  options_.comparator = test::Uint64Comparator();
+  std::vector<std::string> keys;
+  for (uint64_t i = 0; i < kNumKeys; i++) {
+    keys.emplace_back(EncodeAsUint64(i));
+  }
+  CreateFile(sst_name_, keys);
+
+  SstFileReader reader(options_);
+  ASSERT_OK(reader.Open(sst_name_));
+  std::unique_ptr<Iterator> iter;
+  {
+    // Make sure ReadOptions go out of scope ASAP so we know the iterator
+    // operations do not depend on it.
+    ReadOptions ropts;
+    iter.reset(reader.NewIterator(ropts));
+  }
+  iter->SeekToFirst();
+  while (iter->Valid()) {
+    iter->Next();
+  }
+}
+
 TEST_F(SstFileReaderTest, ReadFileWithGlobalSeqno) {
   std::vector<std::string> keys;
   for (uint64_t i = 0; i < kNumKeys; i++) {