LibGUI: Ensure GlyphMapWidget selection resets when requested
Previously selection reset was ignored on active glyph change if the
old glyph equaled the new one. This was an intentional behavior that
allowed selections to resize by dragging the focused glyph, but has
proved more counterintuitive than useful.
Now the widget behaves like other text selection controls: selections
can be reset by clicking anywhere in them or shift can be held to
grow the selection.