Move MS predefined type_info out of InitializePredefinedMacros

Instead of keeping it in amongst the macros, build the declaration at Sema init
the same way we do with other predeclared and builtin types.

In practice this means the declaration is marked implicit and therefore won't
show up as an unwanted user-declared type in tooling which has been a
frequently reported issue (though I haven't been able to cook up a test).