collections: Remove all collections traits

[alexcrichton]

As part of the collections reform RFC, this commit removes all collections
traits in favor of inherent methods on collections themselves. All methods
should continue to be available on all collections.

This is a breaking change with all of the collections traits being removed and
no longer being in the prelude. In order to update old code you should move the
trait implementations to inherent implementations directly on the type itself.

Note that some traits had default methods which will also need to be implemented
to maintain backwards compatibility.

[breaking-change]
cc #18424

[rust-highfive]

Warning

• These commits modify unsafe code. Please review it carefully!

[Gankra]

I'm building off this specualtively. Got this:

C:\users\alexis\documents\github\rust\src\libstd\rand\os.rs:133:9: 133:37 error: unresolved import `core_collections::Collection`. There is no `Collection` in `core_collections`
C:\users\alexis\documents\github\rust\src\libstd\rand\os.rs:133     use core_collections::Collection;
                                                                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:\users\alexis\documents\github\rust\src\libstd\dynamic_lib.rs:282:9: 282:32 error: unresolved import `collections::MutableSeq`. There is no `MutableSeq` in `collections`
C:\users\alexis\documents\github\rust\src\libstd\dynamic_lib.rs:282     use collections::MutableSeq;
                                                                            ^~~~~~~~~~~~~~~~~~~~~~~
C:\users\alexis\documents\github\rust\src\libstd\rt\backtrace.rs:660:9: 660:37 error: unresolved import `core_collections::Collection`. There is no `Collection` in `core_collections`
C:\users\alexis\documents\github\rust\src\libstd\rt\backtrace.rs:660     use core_collections::Collection;
                                                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 3 previous errors

[Gankra]

@alexcrichton Ah, these are #[cfg(windows)] things. That explains why you missed 'em.

[alexcrichton]

Thanks for the heads up @gankro! I've updated to hopefully compile on windows as well now

[Gankra]

ack, and now you have merge conflicts. So many collection changes 😭

[aturon]

I don't understand how this comment relates to the rest of the file.

[sfackler]

Needs a rebase

[Gankra]

Look, @bors. I know you really like generic collection programming, but you've gotta let go. Just... come on. 😞

[Gankra]

Awesome! Building my patch now.