swift234

Move mangling logic for type metadata and field offset into Mangler.

...so that the debugger can use it too. We may end up needing to move more
things from LinkEntity to Mangler in this way, but this is the baseline for
what's needed to properly display private types.

The suffix "Full" here is intended to represent that the Swift prefix "_T"
is included already; if there's a better name for this I'd be glad to change
it.

rdar://problem/18353463

Swift SVN r22031