[feat] Snap windows to borders of other windows to form a window group

Example: https://www.nurgo-software.com/products/aquasnap#:~:text=Window%20snapping

Motivation: Zone-based window management is useful for fixed layouts, but dynamic layouts benefit much more from automatically detecting existing window borders.

The issue names no files, tests, or entry points. Start by locating the window-snapping and layout-management entry points in the TypeScript GNOME Shell extension, then compare the requested behavior with the linked AquaSnap example. Done means windows can snap to the existing borders of other windows and form a window group.

Written by the indexing model from the issue text.