Log an error if a keyboard shortcut uses keys not in the current keymap

[jasongrout]

Currently a user is not warned if they are using keys not in the current keymap. It would be helpful if an error is logged to the console (if not thrown outright) if a commands keybinding is registered that uses keys not in the keyboard layout.

I think it might be enough to check in https://github.com/phosphorjs/phosphor/blob/master/packages/commands/src/index.ts#L1028, or perhaps in

phosphor/packages/commands/src/index.ts

Line 1178 in 8d99dbc

function createKeyBinding(options: CommandRegistry.IKeyBindingOptions): CommandRegistry.IKeyBinding {

if each key is a valid key in the keyboard layout using the getKeyboardLayout().isValidKey() function:

phosphor/packages/keyboard/src/index.ts

Lines 33 to 40 in 8d99dbc

	/**
	* Test whether the given key is a valid value for the layout.
	*
	* @param key - The user provided key to test for validity.
	*
	* @returns `true` if the key is valid, `false` otherwise.
	*/
	isValidKey(key: string): boolean;

We had this come up in jupyterlab/jupyterlab#6027, where the user used "Up" instead of "ArrowUp". It would have been useful if there was an error in the console about an unrecognized key.