* Allow status items with error background color (fix #110214)

* rename to statusBarItem.errorBackground

* address feedback and add error colors

* address feedback

The currrent comment says that it's only supported on macOS. It it now supported
on other platforms so this updates the comments accordingly.

Not possible to explicitly change the foreground text color for widgets. Fixes microsoft/vscode#76274

* Adding setting to control the background color for the active tab in an unfocused editor group

* Adding style fixes for unfocused container group when shrink mode is enabled in tab sizing

* fine-graining the selectors to correctly address the unfocused active tab

* move tab unfocused bg color and use current active background values as defaults

* extracting CSS selectors into a generator function to collect common code and reduce redundancies