WorkspaceEdit: Clarify how operations on same URI are applied

[aeschli]

Testing #42334

WorkspaceEdits now can also express resource, creation, renames and deletes. An interesting aspect is how operations on the same resource are handled.
E.g. edits followed by renames followed by more edits
The API spec mentions something about grouping of edits for the same resource.
Not really clear to me what happens with:
edit resA, rename resA -> resB, create resA, set resA

In order to keep things well defined, I'd suggest to always collect the changes in the order they were announced and apply them exactly the same way.