Use precise scrolling values

Since SDL 2.0.18, the amount scrolled horizontally or vertically is
exposed as a float (between 0 and 1). Forward a precise value to the
Android device when possible.

Refs <https://wiki.libsdl.org/SDL_MouseWheelEvent>
Fixes #3363 <https://github.com/Genymobile/scrcpy/issues/3363>
PR #3369 <https://github.com/Genymobile/scrcpy/pull/3369>

Signed-off-by: Romain Vimont <rom@rom1v.com>