* 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

Part of #74250

- Extend `Disposable` in classes where it makes sense
- Use `DisposableStore` for lists of disposables
- Make `combinedDisposable` take arguments instead of an array (so that you can't pass in an array and then modify the array after the fact)

more consistency

Fixing errors related to https://github.com/microsoft/TypeScript/issues/31380

This reverts commit 0e02825e.