This PR starts work on the Client Game Test API. The API should be considered experimental and breaking changes in the future are expected.

• Renames client auto tests to client gametests
• Moves the existing client gametest code to its own experiment Fabric API module
• Creates an entrypoint for client gametests which starts running when the client has loaded and starts ticking (no gametest would want to run before this point anyway, and gets rid of the hack which waits until the client thread can start accepting tasks)
• Moves functionality out of FabricClientTestHelper into non-static methods in ClientGameTestContext
• Adds an input system that allows gametests to simulate keyboard and mouse inputs (including via key bindings)
• Unlinks GLFW input handlers from the game, preventing real user input from interfering with tests.