swift234

Debug Info: Retrieve the layout information of exploded values from the
explosion schema rather than from the debug type information and retire
a bunch of heuristics that are no longer necessary.

To enable this, this commit also includes a bugfix to debug info for
opaque data structures with the correct size and alignment information.

<rdar://problem/21470869+22707597>

This reapplies ad4f065ad6 and 7e489db9 after fixing the problem
uncovered by this commit in 5726370c1.