Merge editor: integrate the editable result editor like a normal text editor

[bpasero]

Testing #150389

A diff editor today when you open it behaves in many ways like a normal text editor, for example:

• Initial language features in the Result editor would be great #150868
• Merge Editor: language status should show #151136
• you can goto definition and the resulting jump will remain within the editor (this is done via ICodeEditorService actually)
• you can close a dirty diff editor without being asked to save provided that the file is opened in a normal editor somewhere else

Maybe we should split this issue up into individual things, there is probably not a single fix for all these items, but bringing up for discussion.

[jrieken]

I believe most points of this issue are because of the disablement of editor contributions

you can close a dirty diff editor without being asked to save provided that the file is opened in a normal editor somewhere else

This is valid but I believe only works because the workbench has deep knowledge about the concept of side-by-side editors. I was wondering if the merge editor should be side-by-side of side-by-side to get this working properly. Let's discuss offline

[jrieken]

Closing this in favour of #150868 and #151024