2b6a8b2d4c
Rather than hard-coding the type of incoming events to mouse, and synthesizing a primary button press for kDown/kUp, expose device kind and buttons in the API. For backwards compatibility, if the type is not set, the old behavior is used. If an embedder sets the type to mouse explicitly, however, they must also set correct button information. For the touch type, the API abstracts away the framework's internal expectation that a button is set for touch down/move for simplicity. Fixes flutter/flutter#32854