Move traitsui.testing._exception_handling.reraise_exceptions here to be made public?

The `reraise_exceptions` in TraitsUI is generally useful for writing tests to ensure the test suite does not just crash prematurely (e.g. Qt Abort trap) and all the unexpected exceptions cause the test suite to fail. The function is here:
https://github.com/enthought/traitsui/blob/770e94346e06dc70909f125ba7237edce90872da/traitsui/testing/_exception_handling.py#L36-L74

It is clear that the function may be useful for any GUI event loop related tests, and that is why it is kept private to TraitsUI, just so that it can be moved and be made public in Pyface one day.