swift234

Clean up tuple and extract SILBuilder stuff:
- Introduce emitTupleExtract / emitStructExtract, which fold when their operand is a tuple/struct.
- Rename SILBuilder::createTupleExtractInst -> createTupleExtract, "Inst" isn't used as a suffix.
- Switch capture promotion and DI to use the new functions.

This trims 300 lines out of the stdlib.


Swift SVN r9897