Put mocks to directory structure mimicking project structure.

Remove symlinks and make codebase use common modules instead.

Add tests for initialization and teardown for all input methods.

Add memory and data-related implementations for handling game data.

Use consistent integer types for mocks.

Properly mock video function dependencies.

Update input tests.

Implement tests for joystick axis, hat, and button events.

Add third-party mocks, specify mock files.

/? Do we need first-party mocks in their own files, or can we provide a
mock flag in the implementation files already?