Addresses two improvements to `Snap to Grid` suggested in #73993:
- Make 'Absolute Grid Snapping' a new Snap Mode
- Snap to Grid in Perspective View performed at ground level
Implementation details:
- The old "Absolute Grid Snap" option has been removed.
- Snap to Grid has no symbol, unless we are in `Set Snap Base` mode.
- In side view, Snap to Grid is not done at ground level.
- If `Snap With` is `Closest`, Snap to Grid uses the transform pivot instead.
This keeps the behavior closer to the previous "Absolute Grid Snap".
Germano Cavalcante