Check return value bounds: update tests

[kkjeer]

This PR updates test files to account for the new compiler behavior in checkedc-clang/1150: checking that the inferred bounds of a return expression imply the declared bounds (if any) for the enclosing function.

The test updates fall into three different categories:

1. Adding expected errors for functions with declared bounds that return a value with unknown bounds that were previously marked with TODOs. There were six errors of this kind: one in bounds_decl_checking.c and five in pointer_types.c.
2. Adding expected errors for functions with declared bounds that return a value with unknown bounds that were not previously marked with TODOs. There were two errors of this kind: one in checked_scope_interfaces.c and one in interop_type_annotations.c
3. Adding expected errors for return value bounds and declared function bounds that had free variables. There were five errors of this kind: all in bounds.c.

[sulekhark]

LGTM! Thanks!

[sulekhark]

LGTM!