[InstallAPI] Collect frontend attributes & ObjCInterface decls (#83378)

* This patch introduces a container class, for holding records and
attributes only collectible from the clang frontend, which is a subclass
of `llvm::MachO::RecordsSlice`
* This also prunes out collecting declarations from headers that aren't
considered input to installapi.
* Uses these constructs for collecting global objective-c interfaces.