Add support to show close button for active tab only.

[kovdu]

This MR introduces activeOnly for the showCloseButton theme option causing the close button only to appear on the active tab.

This is more or less following the approach explained here https://github.com/orgs/microsoft/projects/686/views/2?pane=issue&itemId=19775774 which indeed just works 😄 .

You notice when switching theme the close buttons is back on all tabs again as well.

Closes #13672

I didn't check specific unit tests for this. I hope by making this MR the pipeline will show if I broke something. Or just let me know if you want me to add something specific for this.

[zadjii-msft]

Yep that's literally how I'd do it 😝 Thanks!

[carlos-zamora]

Love it! Thanks for the contribution! Please be sure to...

• update the schema
• update the docs

Verified that this works if you change the showCloseButton setting via hot reload.

[carlos-zamora]

Demo

Small demo of the result:

NOTE: removed the demo from the PR body so that the commit history is a bit cleaner

[carlos-zamora]

@kovdu I'm not going to merge this yet to give you some time to apply/respond to my comments, but the PR is good to go! Again, thanks for the contribution!

[kovdu]

Thanks for the feedback @carlos-zamora .

Fixed your remarks, updated profiles.schema.json to reflect the new option and created an MR for updating the documentation as well: MicrosoftDocs/terminal#660. Not sure what the process is to get that one merged though.

Also verified the new value is correctly applied when hot reloading the settings file.