Raw mouse movement is unaccelerated and unclamped by screen boundaries,
and does not relate to any position on the screen.
It is useful in certain situations such as draggable values and 3D
cameras, where screen position does not matter.
https://github.com/emilk/egui/assets/1700581/1400e6a6-0573-41b9-99a1-a9cd305aa1a3
Added `Event::MouseMoved` for integrations to supply raw mouse movement.
Added `Response:drag_motion` to get the raw mouse movement, but will
fall back to delta in case the integration does not supply it.
Nothing should be breaking, but third-party integrations that can send
`Event::MouseMoved` should be updated to do so.
Based on #1614 but updated to the current version, and with better
fallback behaviour.
* Closes#1611
* Supersedes #1614
b8048572e8