[Feature Request] Indicator of stacked windows (occupying the same tile) and/or creating tabs to access stacked windows

**Describe the feature you'd like**
Adding these two ideas in one since they both solve the "problem" of unknown stacked windows. Could have both of these optional for users
1) Some window indicator if there is another window occupying the same tile. This could be even perhaps another border color. for example, if stacked there is a red border, but when a window is alone in a tile the border is green (current functionality), or no border when alone.
2) When stacked the windows get a tab bar at the top to switch between them. See Forge or Pop_OS! tiling which does tabbed stacks.

**Additional context**