swift234

[lower-aggregate-instrs] Teach TypeLowering how to produce "lowered" copy values without bugs this time = ).

Originally there was a emitLoweredCopyValue method in TypeLowering, but it was
removed by Chris in r11353 since SILGen was no longer using it and it had bugs.
This method is useful for SILLowerAggregateInstrs, so I resurrected it, fixing
the bugs therein.

The bug was that emitLoweredCopyValue was not reforming aggregates correctly
since it was only considering non-trivial values. The new implementation passes
in all child values, but only recursively lowers the non-trivial children. This
does create an extra tuple_extract, struct_extract for trivial arguments, but
those are easily cleaned up by later dce.

Swift SVN r11753