Templatize Relative*Pointer on offset type.
Templatize Relative*Pointer on offset type.

We usually want to use 32-bit offsets, since we use them to reference other objects within the same small-code-model image. However, for data structures that are both compiler-generated and runtime-allocated, we may want to save the relocation in compile time, but need a full-width offset to be able to relatively reference things from the heap. NFC yet.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift