Query: Don't read default value from databases

[smitpatel]

In 3.x when reading values from database, we started returning default value of expected type if the value was null in the database. That means if we needed to read int then database value was null then we got 0 back. Which is not correct as we should throw exception for the case.

The fix here is,

• All value read from databases are of nullable type as database can return null.
• Since all the bindings with database are nullable now,
  • When doing member access we add null check and return nullable of return type
  • When doing method call we add null check for instance. All parameters we convert to original types.
  • All other expressions, where they need to match the type to reconstruct the original tree, adds convert nodes.
• For translation of Single/SingleOrDefault (and friends)
  • For scalar subquery
    • We add coalesce with default value for SingleOrDefault
    • We don't add coalesce for Single case and assume there will be non-null value coming out of database which we will try to assign.
  • For non-scalar subquery
    • We add default value in client side in shaper for SingleOrDefault
    • We throw exception Sequence contains no elements for Single case
  • Above rules are only when not returning entity type. When returning entity type, we don't have enough information to differentiate the case. Also above behavior is just side-effect of assigning values to properties which cannot take null values.
• When doing DefaultIfEmpty over a non-reference type, navigation expansion will add client side coalesce so that we can move Selector after DefaultIfEmpty

Resolves #20633
Resolves #20959
Resolves #21002

[smitpatel]

Pending TODOs (all done)

• Still working on replicating same for InMemory/Cosmos
• Update or remove tests which were incorrect due to 3.x behavior
• Add exception messages in resources file.