[RegistryPreview] Rethink commandbar to increase density

Description of the new feature / enhancement

There are too many rounded corners in the page, and the segmentation is too messy. By aligning to the design file of FDS, referring to the first-party design such as Notepad, we can achieve-

The segmentation from edge to edge makes the design look simple, neat and crisp. Match the first-party design to improve the unity. Reserve the possibility of adding multi-tab support in the future.

Scenario when this would be used?

Supporting information

https://www.figma.com/community/file/1159947337437047524/windows-ui-3

According to the official design specification, the standard title bar-toolbar-content view is as shown in the figure. There is no separate toolbar rounded background.

You can find it in the official Figma file