Migrate tests to not use fixtures as much as possible

[Ruin0x11]

After learning more about the IDEA codebase I've found better ways to run tests without needing to rely on as many on-disk fixtures. In many cases files can be instantiated using the in-memory test fixture. This allows the tests to not have to reference cryptic offsets that only make sense by opening the fixture file and going to the offset referenced. All the information needed to understand the test can be contained in the test itself.