Revisit editorOpenWith living on its own

[bpasero]

I feel the editorOpenWith.ts thing needs to go away and move to respective services. It seems wrong to me that you pass in an editor group to operate on instead of having this exposed from the IEditorGroupService. Here is my thinking:

• add a new method to IEditorGroup (e.g. openEditorWith)
• clients will use IEditorGroupService.getGroup().openEditorWith(...)
• this method should also include the necessary dialog prompts for dealing with unsaved editors (from Prompt user with dialog if triggering open with on unsaved file #115264)

As for the remaining pieces of editorOpenWith.ts we can simply move them into src/vs/workbench/common/editor.ts at the end into a new folded region.

[bpasero]

This is now outdated and please see the proposal in #100281. Feel free to close.

[lramos15]

Closing in favor of #100281