Expose rectangular tabs to Settings/Thorium Experiments menu

Is your feature request related to a problem? Please describe. Not related to a problem, more a feature exposure request. Thorium has a rectangular tabs feature (flag thorium://flags/#rectangular-tabs), but it isn't exposed as an easily accessible user-facing customization feature.

Describe the solution you'd like, including relevant patches or source I suggest adding such an option in the thorium://settings/appearance settings page. Likely named something like "Rectangular Tabs" or something like that. Alternatively, the feature could be exposed in the "Thorium Experiments" menu, or a combination of both.

I tested the flag itself for multiple days and I've not encountered issues with it so far on Windows 11 23H2. The rationale boils down to: Thorium already is the more customizable fork of Chromium, so it would make sense to make Thorium more customizable.

Did you read the FAQ? https://thorium.rocks/faq Yes, I did.