Add "tree-style-tab" attribute to main-window

[benzBrake]

Is your feature request related to a problem? Please describe.

I want to write customize css that hide horizontal tabsbar when Tree Style Tab is opened.

Describe the solution you'd like

When Tree Style Tab open, main-window's attribue "tree-style-tab" would set to true, else set to false.

The effect can refer to the video

https://user-images.githubusercontent.com/11323774/193781733-eb65b668-8738-49ca-97b9-55cb512c73dc.mp4