Test: Custom editor finalization

[mjbvz]

Test for #77131

• Windows @alexr00
• Linux @9at8
• MacOS @sandy081

Complexity: 5

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Summary
The custom editor API has been finalized this iteration. There have been no major changes to the API however we've fixed a number of bugs around custom editors, and we would also like to have another set of testers to take a look at this API.

Note: If you have previously tested custom editors, consider reassigning it to someone who does not have experience with the API

In this exploratory test plan item, I'd like you to try implementing a basic custom editor as if you were an extension developer (possibly try embedding an existing html+js library into a custom editor).

Links

• Finalized API
• Extension sample (You can build on these for your custom editor implementation)
• Documentation

Areas to focus on

• API docs and intellisense (for both the TS api and contribution point)

  Do they make sense? Anything missing?

• Editing and basic saving

  Make sure undo, redo, and revert work for CustomEditor and CustomTextEditor. Make sure the VS Code UI updates correctly and that all fields on CustomDocument are updated correctly. Are there anything that prevents you from implementing your custom editor or that would simplify things?

• Hot exit and backup

  Make sure custom editors are properly restored when the window is reloaded

• The Reopen with command the the workbench.editorAssociations setting

  If there are multiple custom editors for a single resource, make sure you can use workbench.editorAssociations to configure which one is used by default

• Try finding cases where a custom editor behaves differently from our normal editors

  Especially around renaming/deleting files and dirty states