[CoroElide] Remove fallback for frame layout determination

Only determine the frame layout based on dereferenceable and align
attributes, and remove the type-based fallback, which is incompatible
with opaque pointers. The dereferenceable attribute is required,
while the align attribute uses default alignment of 1 (commonly,
align 1 attributes do not get placed, relying on default alignment).

The CoroSplit pass producing the resume function adds the necessary
attributes in https://github.com/llvm/llvm-project/blob/7daed359111f6d151fef447f520f85ef1dabedf6/llvm/lib/Transforms/Coroutines/CoroSplit.cpp#L840,
and their presence is checked in coro-debug.ll at least.

Differential Revision: https://reviews.llvm.org/D120988