LowerTypeTests: Split the pass in two: a resolution phase and a lowering phase.

This change separates how type identifiers are resolved from how intrinsic
calls are lowered. All information required to lower an intrinsic call
is stored in a new TypeIdLowering data structure. The idea is that this
data structure can either be initialized using the module itself during
regular LTO, or using the module summary in ThinLTO backends.

Differential Revision: https://reviews.llvm.org/D28341

llvm-svn: 291205