mpv's window-dragging feature doesn't work in awesome

[sammoth]

Output of awesome --version:

awesome v4.3 (Too long)
• Compiled against Lua 5.1.4 (running with LuaJIT 2.0.5)
• D-Bus support: ✔
• execinfo support: ✔
• xcb-randr version: 1.6
• LGI version: 0.9.2

How to reproduce the issue:

Open a video in mpv with it floating and its window-dragging feature enabled, eg mpv --window-dragging xxx.mp4. It's supposed to let you grab the window with the left mouse button on the picture and drag it around.

Actual result:

The window doesn't move

[psychon]

Assuming I followed the code correctly:

• --window-dragging sets some allow_win_drag variable: https://github.com/mpv-player/mpv/blob/05fb6f906de25016faff2bdedd1f47f1e4077554/input/input.c#L202 (which, by the way, defaults to "enabled" https://github.com/mpv-player/mpv/blob/05fb6f906de25016faff2bdedd1f47f1e4077554/input/input.c#L220)
• This variable is used here: https://github.com/mpv-player/mpv/blob/05fb6f906de25016faff2bdedd1f47f1e4077554/input/input.c#L1069-L1076
• And that function is used here: https://github.com/mpv-player/mpv/blob/93a6308bb762dc1c43e0301c7b6e977078bead9c/video/out/x11_common.c#L1168-L1187

Looks like this uses _NET_WM_MOVERESIZE. Assuming I am right, this is a duplicate of #2140.