[Decorations]: Emit old and new URI's to ensure ProvideWrapper.data correctly updated

[colin-grant-work]

What it does

In #10846, I misunderstood the behavior of the DecorationProviderWrapper class and believed that it would respond correctly to a DecorationsProvider emitting only the currently decorated URI's. In fact, it needs to receive a list of both removed and changed URIs.

How to test

1. Open a file.
2. Create some problems.
3. Problem decorations should appear in the file tree.
4. Save the file.
5. Git decorations should appear in the file tree. (assuming you're in a tracked repository)
6. Revert the file to its old state.
7. The git decorations should disappear from the file tree, and if there are no problems left in the file, the problem decorations should disappear from the file tree.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

I confirm that the changes fix the issues present on master where the decorations do not update 👍