Implementation of NNBD runtime checks for weak mode support

[a-siva]

List of tasks

• Annotated NNBD Types in VM Annotated NNBD Types in VM #38842
• Infrastructure work in VM type objects for NNBD
• Implementation of runtime checks for weak mode support
• type equality intrinsics
• Check required named parameters in type tests
• Check required named parameters during resolution
• Update inlined type testing code
• Update type testing stubs

[a-siva]

Some tests that are currently failing related to this issue

language/nnbd/static_errors/unchecked_use_of_nullable_test/114
language/nnbd/static_errors/unchecked_use_of_nullable_test/74

[liamappelbe]

Looks like the functions that those 2 lines sit in are never actually called from main, so we're only getting compile time errors for those functions. I'll update the test to call them.

[a-siva]

I don't think we are done with this issue (please see the original description that lists the set of tasks needed).