Use FlaxEngine Asserts

The FlaxEngine comes with a class full of assertion functions `FlaxEngine.Assertions.Assert`. So we don't really need to ship our own.

The only exception here is the pass assertion. `public static void Pass() => throw new SuccessException();`

Inspect the project's assertion implementation and its usages, then compare them with FlaxEngine.Assertions.Assert. Replace the shipped assertion functions with the engine's equivalents while preserving the Pass behavior described in the issue. Done means the redundant assertions are no longer needed and existing tests still pass.

Vom Indexierungsmodell aus dem Issue-Text verfasst.