Cancelling opening a folder from a multi-root unsaved workspace corrupts the current worksapce (fixes #42799)

* Allow middle mouse click to open file entry in the background

* Remove unnecessary assignment

* Remove unnecessary payload

* Go with preferred way

* 💄

* Fix #39417

* Use pseudo elements instead of mask-image so that labels retain subpixel AA

* Use ellipsis and disable fade for HC theme, and support hover colours

* Make requested changes and start on fixing transparency issue

* Merge all colours underneath tabs to fix transparency issue

* Rename color function, move workbench background into themes

* do not allow to change workbench background

* 💄

* fix npes and clean up

* fix class names

* remove blank line

* Open issue reporter in same display as workbench

* Styling updates

* Increase url length limit

* normalize extension ids before checking isEnabled

listen to onDidFocus and keep track of whether focus is inside the tree

and add displayIdx

Fixes #42058

Fixes #42482

Fixes #42764