Shift+Tab ran Tab's command and hid the toolbar and the Control bar
along with the panels. egui matches a chord without Shift when Shift
is also held.
A new UI command, window.panels (default Shift+Tab), shows and hides
the dock and the floating panels and leaves the toolbar and the
Control bar as they are. The shortcut table tries chords with more
modifiers first, so Tab's chord no longer takes Shift+Tab. Hiding the
panels with Tab or Shift+Tab also closes a panel popped out of the
icon column, which stayed on screen at the window's right edge.
Docs: docs/target-app-parity.md.