Fix ARCSequenceOpts handle of is_escaping_closure
Handle is_escaping_closure like an RC-checking instructions. It looks
like it "may-decrement" RC because: if the object must be live after
the instruction and the subsequent local release, then it expects the
refcount to be greater than one. In other words, do not remove a
retain/release pair that spans an is_escaping_closure
instruction.
This would otherwise fail to catch closures that are returned
from the function.
The following retain/release pair cannot be removed:
%me = partial_apply
retain %me
is_escaping_closure %me
release %me
return %me
Fixes <rdar://problem/52803634>
