[coro async] Disable lifetime.start sinking for ABI::Async and ABI::Retcon

It does not handle loops correctly i.e it moves the lifetime.start
intrinsic into a loop rendering the stack object as not alive for part
of the loop.

```
  entry:
    %obj = alloca i8
    lifetime.start(%obj)

    br loop

  loop:
    coro.suspend()
    escape(%obj)
    cond_br %cond, label %exit, label loop

    br loop

  exit:
    lifetime.end(%obj

```

After sinking:

```
  entry:
    %obj = alloca i8
    br loop

  loop:
    coro.suspend()
    lifetime.start(%obj)
    escape(%obj)
    cond_br %cond, label %exit, label loop

    br loop

  exit:
    lifetime.end(%obj

```

rdar://83411917

Differential Revision: https://reviews.llvm.org/D110953