[Debug] [Coroutine] Adjust the scope and name for coroutine frame

Previously the scope of debug type of __coro_frame is limited in the
current function. It looked good at the first sight. But it prevent us
to print the type in splitted functions and other functions. Also the
debug type is different for different coroutine functions. So it makes
sense to rename the debug type to make it related to the function name.

After this patch, we could access the coroutine frame type in a function
by `function_name.coro_frame_ty`.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D127623