Summary:
We have a custom STUB_VIEW_ASSERT that helps debugging stub view issues on platforms (like iOS) where flushing logs around assert-time isn't 100% guaranteed.
Move that logic into react_native_assert since it's generally useful.
Changelog: [Internal]
Reviewed By: mdvacca
Differential Revision: D26567218
fbshipit-source-id: 79f5ae66fc65a0af48dbcf4c7204ac8245911cb0