Add setting to disable resize overlay (COLS × ROWS)

### Description of the new feature

The recently merged resize overlay (PR #20059) shows terminal dimensions in the center of the window when resizing or changing font size.

While this is a nice feature for many users, I find it visually distracting :(
— I don't need to see the column/row count during resize, and the overlay clutters the experience.

Request for example: Add a setting (e.g. "experimental.showResizeOverlay": true) to settings.json so users can disable this overlay and/or add setting in SUI.

Default can remain true — I just want the option to turn it off.

Thanks!

### Proposed technical implementation details

_No response_

Start by reviewing the resize overlay introduced in PR #20059 and tracing how settings.json and the SUI expose related options. Add a setting that disables the overlay while keeping it enabled by default, then verify that resizing and font-size changes respect the setting.

Written by the indexing model from the issue text.