video: Added key conversion from other layouts to english one

[dimok8a]

Fixed the bug, described in issue #45.
Bug: if you have a non-english layout (like Armenian, Arabic or etc.), your key bindings don't work.
I tested this using 3 layouts (Armenian, Arabic and Russian), and it works well. However, it works only with keys related to English alphabet (lower and upper cases).

[github-actions]

Download the artifacts for this pull request:

Windows

• mpv-i686-w64-mingw32
• mpv-x86_64-w64-mingw32

[kasper93]

This needs to be rebased and prefix should be win32: ...

I have no idea if this is correct solution to the problem. @na-na-hi maybe you know?

[na-na-hi]

This approach is improper and should be closed. It only deals with English letters, which is insufficient.

I have considered this problem before and I think the right way to do this is to use scancode for layout-independent keyboard handlings. I think this could be done by adding a new suite of keys SCANCODE_XXX.

Also this PR doesn't provide an option to disable this behavior. mpv (and mplayer) has always been dependent on keyboard layout by default.

[kasper93]

I agree this looked to me not complete and that's why I ask. @dimok8a closed for now, feel free to reopen if you came up with better solution.