Lazy loading checked if the ClangDecl was hidden, but loading all
members did not. Let's make loadAllMembers() behave like the lazy
path, and fix some of the mock SDKs in the test suite.
When trying to figure out errors from an import failure, the nullability
completeness warnings would clutter the output making it difficult to
identify the errors. Sprinkle the declaarations with
`_Null_unspecified` to maintain the current nullability semantics and
silence the warnings. NFC.
Otherwise, the lookup table for "CGColor" has two entries, because of
this:
typedef struct CGColor *CGColorRef;
and that interferes with our ability to import things as members of
"CGColor" (as opposed to "CGColorRef"), which affects the fix-its we
generate when you try to use the non-member form.
This isn't necessarily the best long-term solution (as noted in the
FIXME) but it is expedient and won't break any current users.
More rdar://problem/26347297
