fix: workspace/didDeleteFiles multiple deletions in the same folder

[LQR471814]

The handling logic for workspace/didDeleteFiles does not properly handle multiple file deletions in the same folder.

Consider the following case:

foo/
  file1.md
  file2.md
  file3.md

1. Let file3.md reference (via wikilink), both file1.md and file2.md.
2. Both file1.md and file2.md are deleted, this is notified via workspace/didDeleteFiles.
3. Marksman loops through [file://.../file1.md, file://.../file2.md]
   1. The first time, state -> folder with file1.md -> folder without file1.md ([file2.md, file3.md])
   2. The second time, state -> folder with file2.md -> folder without file2.md ([file1.md, file3.md])
4. Thus your new state ends up being [file1.md, file3.md], not the expected [file3.md].

The fix is just to have it search newState and derive new folders from it rather than the old state.