* Don't invalidate the lookup cache in 'getOrCreateSynthesizedFile()'
Adding a synthesized file itself doesn't introduce any decls. Instead,
we should invalidate the right after the actual declrations are added
in the file
* Remove 'SourceLookupCache::invalidate()' method. It was just used
right before the destruction. It was just not necessary
* Include auxiliary decls in 'SourceLookupCache::lookupVisibleDecls()'
Previously, global symbol completion didn't include decls synthesized
by peer macros or freestanding decl macros
* Include "auxiliary decls" in visible member lookup, and visible local
decl lookup
* Hide macro unique names
rdar://110535113
