Keyboard layout popup

### Feature Description

Please add a pop-up window showing the selected language layout so it's clear which language is selected.
Thanks)

### Use Case

In full-screen apps, it's unclear which language is selected because the bar is hidden

Also, if it's not too much trouble, please add different styles for this feature. (These are just plans for the future.)
Alternatively, you could add keyboard-switching themes to the theme store. (But that's more a matter of customization than developing new functionality.)
BTW, Thank you for your support and for updating your product)

### Compositor(s)

All compositors

### If Other, please specify

_No response_

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

No files, tests, or entry points are named. Start by locating the existing keyboard layout indicator and the code shared across the listed compositors, then determine how a popup can show the selected language and how its styles should be customized. Done means the popup works in full-screen apps across all compositors and its presentation is defined.

Written by the indexing model from the issue text.