GD-156: Add an exception hook to report exceptions as test failures that are caught by Godot

[MikeSchulze]

Why

see https://github.com/MikeSchulze/gdUnit4Net/issues/156

What

• added an exception hook to redirect Godot caught exceptions to report as test failure.
• improved ThrowsExceptionAttribute to validate for source file and line
• fixed issues with using ThrowsExceptionAttribute, it was missing to validate for expected exceptions after test execution.