This PR fixes #110694

Diff editors can have a tab label that is too long in some cases. This PR implements the ability for tabs to have multiple labels, each with separate code icons and shortened paths, and makes use of that for diff editors.

The alternative to this would be to just shorten the paths but keeping the current way of labeling. I have implemented that as well. See #110694 and master...goldst:shorten-diff-title-A for details.

Test this by opening two files with the same name but different paths, then ctrl+shift+p -> compare active file with...

Overview of the most important changes from a technical point of view:

• add getNames and getDescriptions to IEditorInput so editors can have one or multiple labels. Implement these in EditorInput where they return the name and description, and override them in DiffEditorInput to return all three labels (left editor, compare arrow, right editor)
• change the logic for rendering tabs:
  • tabTitleControl.ts gets all names and descriptions and shortens paths even when there are multiple paths in one label
  • add some classes in label.ts (eg MultipleResourceLabels and ResourceLabelWidgets) that have mostly the same methods as the ones previously in use, but they are a wrapper for multiple objects of the previous classes. Also added some interfaces/parent classes (eg IResourceLabels, IResourceLabelWidget and ResourceLabelGroupBase) to make sure they behave in the same way as the ones used previously.

This PR might have some implications that weren't clear to me, that's why I suggest that it should be reviewed thoroughly. I would also like to have a general yes or no for this approach before I/we fix the merge conflicts.