Improve the debug info for coro-split .resume functions

This patch updates the scope line to point to the suspend point. This
makes the first address in the function point to the first source line
in the resume function rather than the function declaration. Without
this the line table "jumps" from the beginning of the function to the
suspend point at the beginning.

rdar://73386346

Differential Revision: https://reviews.llvm.org/D97345