input.conf: bind MBTN_MID_DBL to resetting pan

Allow resetting pan with the mouse after binding drag to pan to the
mouse.

Author: guidocella

DOCS/man/mpv.rst

@@ -360,6 +360,9 @@ Right click
 Middle click
     Pan through the whole video while holding the button.
 
+Middle double click
+    Reset pan.
+
 Forward/Back button
     Skip to next/previous entry in playlist.
 

etc/input.conf

@@ -32,6 +32,7 @@
 #MBTN_LEFT_DBL cycle fullscreen    # toggle fullscreen
 #MBTN_RIGHT    cycle pause         # toggle pause/playback mode
 #MBTN_MID      script-binding positioning/align-to-cursor # pan the whole video
+#MBTN_MID_DBL  no-osd set video-align-x 0; no-osd set video-align-y 0; no-osd set video-pan-x 0; no-osd set video-pan-y 0 # reset pan
 #MBTN_BACK     playlist-prev       # skip to the previous file
 #MBTN_FORWARD  playlist-next       # skip to the next file
 #Ctrl+MBTN_LEFT script-binding positioning/drag-to-pan # pan around the clicked point