config: implement shortcut latching

toml-spec/spec/spec.generated.json

@@ -438,6 +438,10 @@
         "action": {
           "description": "The action to execute.\n\nOmitting this is the same as setting it to `\"none\"`.\n",
           "$ref": "#/$defs/Action"
+        },
+        "latch": {
+          "description": "An action to execute when the key is released.\n\nThis registers an action to be executed when the key triggering the shortcut is\nreleased. The active modifiers are ignored for this purpose.\n\n- Example:\n\n  To mute audio while the key is pressed:\n\n  ```toml\n  [complex-shortcuts.alt-x]\n  action = { type = \"exec\", exec = [\"pactl\", \"set-sink-mute\", \"0\", \"1\"] }\n  latch = { type = \"exec\", exec = [\"pactl\", \"set-sink-mute\", \"0\", \"0\"] }\n  ```\n\n  Audio will be un-muted once `x` key is released, regardless of any other keys\n  that are pressed at the time.\n",
+          "$ref": "#/$defs/Action"
         }
       },
       "required": []