lua: allow unregistration of idle handlers

DOCS/man/lua.rst

@@ -451,6 +451,11 @@ are useful only in special situations.
     multiple properties at once, you might not want to act on each property
     change, but only when all change notifications have been received.
 
+``mp.unregister_idle(fn)``
+    Undo ``mp.register_idle(fn)``. This removes all idle handlers that
+    are equal to the ``fn`` parameter. This uses normal Lua ``==`` comparison,
+    so be careful when dealing with closures.
+
 ``mp.enable_messages(level)``
     Set the minimum log level of which mpv message output to receive. These
     messages are normally printed to the terminal. By calling this function,

player/lua/defaults.lua

@@ -419,6 +419,16 @@ function mp.register_idle(cb)
     idle_handlers[#idle_handlers + 1] = cb
 end
 
+function mp.unregister_idle(cb)
+    local new = {}
+    for _, handler in ipairs(idle_handlers) do
+        if handler ~= cb then
+            new[#new + 1] = handler
+        end
+    end
+    idle_handlers = new
+end
+
 -- sent by "script-binding"
 mp.register_script_message("key-binding", dispatch_key_binding)