Add a 'type lookup' command. This command is meant to look up type information...

Add a 'type lookup' command. This command is meant to look up type information by name in a language-specific way.

Currently, it only supports Objective-C - C++ types can be looked up through debug info via 'image lookup -t', whereas ObjC types via this command are looked up by runtime introspection

This behavior is in line with type lookup's behavior in Xcode 7, but I am definitely open to feedback as to what makes the most sense here

llvm-svn: 249047