mac: implement VOCTRL_BEGIN_DRAGGING

[Akemi]

only works with left clicks.

overlooked by me and follow up of #13582.
also resolves the possible blocker on #15314.

tested with MBTN_LEFT cycle pause and works as expected now.
also tested with following test script that dragging can be triggered by a script with different binding.

local mp = require 'mp'

local function vo_drag()
    mp.command("begin-vo-dragging")
end
mp.add_forced_key_binding('alt+MBTN_LEFT', vo_drag, {complex=true, event=down})

[github-actions]

Download the artifacts for this pull request:

Windows

• mpv-i686-w64-mingw32
• mpv-x86_64-w64-mingw32
• mpv-x86_64-windows-msvc

macOS

• mpv-macos-13-intel
• mpv-macos-14-arm
• mpv-macos-15-arm

[kasper93]

I cannot test, but otherwise looks ok.