One finger already worked as the mouse. Two or more fingers now make a
gesture instead of fighting over the cursor: two drag to pan and pinch to
zoom about the fingers, three drag to orbit; a quick two-finger tap opens
the context menu, a three-finger tap zooms to the extents and a quick
three-finger swipe up shows the isometric view. While a gesture runs the
drawing area's own pointer handling keeps out, and the press the first
finger started is dropped.
Refs #906
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>