@roblourens This PR fixes #118229. You can test it using these steps:

1. Create the following directory structure:

   foo
   ├── bar
   │   └── baz.txt
   └── .gitignore
   

2. In foo/, run the following command:

   git init

3. Put the following contents in foo/.gitignore:

   baz.txt

4. Put the following contents in foo/bar/baz.txt:

   qux
   

5. Build and run this PR.
6. Open the folder foo/bar/.
7. Run the command Go to File... (Ctrl+P on Linux). Type in baz: the file baz.txt should appear.
8. In the Search sidebar (Ctrl+Shift+F on Linux), type in qux: its appearance in baz.txt should appear.
9. If you opened baz.txt in VS Code in step 7 or 8, run Go to File... again and click the "X" next to baz.txt (it would say "recently opened" in that case).
10. Run the command Preferences: Open Settings (UI) (Ctrl+, on Linux). Type "ignore" in the search bar, then enable the setting Search: Use Parent Ignore Files.
11. Repeat steps 7 and 8: nothing should appear.

I wrote this by piggybacking off of #59717: I searched for the string GlobalIgnoreFiles in the codebase and added similar code for ParentIgnoreFiles alongside each occurrence I found. Please let me know if I missed anything, or if I should add any automated tests to accompany the code changes.