[ClangImporter] Look through __ended_by and __null_terminated (#81630)
Previously we would not import decls containing these types. This was
not an issue, because they can only occur when -fbounds-safety or
-fexperimental-bounds-safety-attributes is passed to clang. When
SafeInteropWrappers is enabled we pass
-fexperimental-bound-safety-attributes to clang however, so these types
can now occur without the user specifying any -Xcc flags.
rdar://151611718