Add options to enable memoryssa for loopsink (defaulting to false,
retaining the original functionality). Expand existing loopsink
testing to also test loopsinking using new pass manager. The option
exposed a bug that was previously fixed for loopsink without
memoryssa. When sinking an instruction into a loop, the source block
may not be part of the loop but still needs to be checked for
pointer invalidation. This is the fix for bugzilla #39695 (PR 54659)
expanded to also work with memoryssa. The bug is only exposed when
all the changes are combined. Just expanding the tests will not show the
bug nor will just enabling memoryssa in loopsink. They have to be done
together to show the bug hence both and the fix are all done in this PR.
Respond to comments after attempted landing: move test for profile
data earlier to avoid unnecessary computations.