This fixes a bug that was preventing keystrokes from being shown on tooltips
for the "Buffer Search" and "Inline Assist" buttons in the toolbar.

This commit makes the behavior of `keystrokes_for_action` more consistent with
the behavior of `available_actions`. It seems reasonable that, if a child view
defines a keystroke for an action and that action is handled on a parent, we
should show the child's keystroke.