Use optimal size alignment

The video was always constrained to use a size that is a multiple of 8.
This was sometimes not necessary (recent codecs only require a video
size that is a multiple of 2 or even 1) and sometimes insufficient (some
codecs require a size that is multiple of 16).

Use the size alignment required by the codec.

Fixes #4949 <https://github.com/Genymobile/scrcpy/issues/4949>
Fixes #6236 <https://github.com/Genymobile/scrcpy/issues/6236>
PR #6746 <https://github.com/Genymobile/scrcpy/pull/6746>