disallow resize window in BSP (single window) or STACKED mode

The mouse modifier and resize should not be allowed while the window is the only window in a workspace in BSP layout. Same for if the window is resizable with a keyboard shortcut, it shouldn't react.

In addition, if the workspace layout is in STACKED mode, all the windows should NOT be resizable.
This will fix UX issues for standalone windows when resizing, as it gives us the idea/confusion if a single window is floating or tiled, or if multiple windows are stacked.

Trace the mouse-modifier and keyboard-shortcut resize entry points, then inspect how BSP workspaces identify a single window and how STACKED layout is represented. Done means resize requests are ignored for a sole BSP window and for every window in STACKED mode, without affecting other layouts.

Written by the indexing model from the issue text.