feat: add play_pause left click command

[Keith94]

Makes left click customizable during regular playback to match upstream mpv.

This PR would allow adding extra things on user's side; for example a script message to show a pause indicator:

play_pause_mbtn_left_command=script-message toggle-pause-indicator; cycle pause

For more context, in my setup I try to avoid showing an indicator when seeking or frame stepping etc so I rely on this script message to show it in specific ways.

[Samillion]

I'm concerned about one scenario conflict.

1. Click (press down) play_pause_mbtn_left_command=cycle pause
2. Unhold click (press up) mp.command(user_opts.play_pause_mbtn_left_command)
3. Possible double cycle?

Since _down is being defined, is step 2. still needed?

    ne.eventresponder["mbtn_left_up"] = function ()
        if state.eof_reached then
            mp.commandv("seek", 0, "absolute-percent")
            mp.commandv("set", "pause", "no")
-       else
-           mp.command(user_opts.play_pause_mbtn_left_command)
        end
    end

[Keith94]

If I remove those lines (else and mp.command) it doesn't work properly. I don't see any conflict here unless I'm wrong.

[Samillion]

But it does override, no? (conflict)

Let me show how to test what I mean, I'm bad at wording things.

In modernz.conf:

play_pause_mbtn_left_command=show-text "test"

Revert back the mp.commandv() but keep bind_buttons() where it is:

    bind_buttons("play_pause") -- dead code. always overridden by event below it
    ne.eventresponder["mbtn_left_up"] = function ()
        if state.eof_reached then
            mp.commandv("seek", 0, "absolute-percent")
            mp.commandv("set", "pause", "no")
        else
            mp.commandv("cycle", "pause")
        end
    end

See what I mean?

[Samillion]

Hmmm. It works though. It's not actually deadcode.

It'll handle other clicks, and it's overridden where needed

bind_buttons("play_pause") -- mbtn_right and shift+mbtn_left (mid) and mbtn_left_up is overridden below
ne.eventresponder["mbtn_left_up"] = function ()
    if state.eof_reached then
        mp.commandv("seek", 0, "absolute-percent")
        mp.commandv("set", "pause", "no")
    else
        mp.command(user_opts.play_pause_mbtn_left_command) -- ensures no conflict
    end
end

[Samillion]

Thank you very much.

Merging.