[11.x] Restore exceptions/errors to test assertion failure messages

[jessarcher]

This PR is an alternative to #51709 that solves the issue of unexpected exceptions and validation errors no longer being included in test assertion failures.

#51709 only solves the issue for status assertions and only includes unexpected exceptions but not validation errors.

I couldn't find anything in PHPUnit that would let me hook in to catch and transform the exceptions globally like we used to, so I've removed the code we had there are localized the responsibility to the TestResponse class. I tried a few different ideas, like wrapping every assertion in a try/catch or inside a closure that gets passed to another method that does the try/catch, but I ultimately felt it was nicer to wrap the Assert class instead.

I have removed some methods and properties that might constitute a BC; however, these were all contained within the testing side of the framework. I'm happy to re-instate them with a @deprecated tag if preferred.