Add an option to control the visibility of the scrollbars used for tabs and breadcrumbs in the editor title area.

Similar options already exists for controlling the visibility of the scrollbars in the editor: editor.scrollbar.horizontal and editor.scrollbar.vertical. They have three possible options: auto, visible, and hidden.

Currently, the behavior of the tabs scrollbar is hardcoded to auto. This new option would make it possible to make these scrollbars always visible or always hidden.

By allowing the tabs scrollbar to be hidden, this would address a longstanding issue that it's easy to accidentally click the blank area of the tiny tabs scrollbar, which unexpectedly scrolls your tabs instead of clicking one. This issue has been raised several times but was closed due to insufficient upvotes.
See: #233864, #111817, #157045, #185625, #219867

I will open a PR that implements this new option.