This introduces Ink.KeyboardShortcut, a utility component used to

display an available keyboard shortcut and optionally register it.
Keys are shown in a form that best matches the local operating system.

On macOS, the Control, Meta/Cmd, Alt/Option, and Shift keys show the

typical symbols, for instance. Some symbols are used in all cases, such

as arrows.
If a KeyboardShortcut is instantiated with an onInvoke and

registry options, then the keyboard shortcut will be registered in the

registry and the onInvoke handler will be called when the shortcut is

pressed. A special onInvoke value of click will trigger a click

event on this component, bubbling up to a parent, which will be useful

for buttons and menu items.

Unit tests pass.
Tested this with in-progress components, ensuring that registration

and event handling worked correctly.