Add Debugger.Break() to Debug.Assert

[BrennanConroy]

Running tests via command line, or running a program (not testing) will crash the process if a Debug.Assert condition fails, and it will pause the debugger if running under one. Both of these behaviors are what I expect and want. However, when running tests via VS testing the Debug.Assert just throws an exception. Which depending on the test could silently pass.

I see #2309 which is when this behavior changed. And while I still think the process should crash when not running under the debugger, I think at a minimum it should break under the debugger so you can see that one of your debug checks is failing.

See https://source.dot.net/#System.Private.CoreLib/src/libraries/System.Private.CoreLib/src/System/Diagnostics/DebugProvider.Unix.cs,18 for example.

[nohwnd]

I would love this to be implemented as exception and also a "note" to the test framework that the test failed even if the exception is swallowed. In retrospect the design implemented was not the best.

[nohwnd]

but this needs to be implemented on each test framework level, so we cannot do anything about it here, except for adding an option to disable the Assert failure captuing.