swift234

Introduce a base class for ApplyInst and PartialApplyInst.

The new base class ApplyInstBase contains APIs that are common for ApplyInst and PartialApplyInst. It allows such optimization passes like generic specializer to treat both instructions in the same way whenever it is possible. Before this change, one had to duplicate and adjust a lot of implementation code in such passes, because ApplyInst and PartialApplyInst were not related to each other in any form.

The existing clients of both classes can continue using the usual APIs. No changes are required. Only new clients, which want to treat ApplyInst and PartialApplyInst in a uniform way, may do so. One of such new clients is the generic specializer, whose adjusted implementation will be submitted in the following commit.

Swift SVN r26581