[Coroutine] [Debug] Insert dbg.declare to entry.resume to print alloca in the...

[Coroutine] [Debug] Insert dbg.declare to entry.resume to print alloca in the coroutine frame under O2

Summary: Try to insert dbg.declare to entry.resume basic block in resume
function. In this way, we could print alloca such as __promise in
gdb/lldb under O2, which would be beneficial to debug coroutine program.

Test Plan: check-llvm

Reviewed by: aprantl

Differential Revision: https://reviews.llvm.org/D96938