Enforce window aspect ratio

Preserve the aspect ratio when resizing the window, so that the window
always matches the device content.

Fixes #2317 <https://github.com/Genymobile/scrcpy/issues/2317>
Fixes #2387 <https://github.com/Genymobile/scrcpy/issues/2387>
Fixes #3460 <https://github.com/Genymobile/scrcpy/issues/3460>
PR #6761 <https://github.com/Genymobile/scrcpy/pull/6761>

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