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 pull request 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.

Release Notes:

- Fixed a bug that was preventing certain keystrokes from being shown in
tooltips.