swift234

SIL: Give TypeLowering support for dependent generic contexts.

Give TypeConverter methods to push and pop a generic context given a set of generic parameter types and requirements from a generic signature. Dependent types lowered in this context can then be lowered using an ArchetypeBuilder seeded with that signature. The TypeLowering objects created for dependent types are put in a special arena which we clear out when we pop the generic context. This sets the stage for allowing us to lower SILFunctionTypes using their interface types.

Swift SVN r11848