Strict null check vs/workbench/services/configurationResolver

[mjbvz]

Part of #60565

Tracks updating vs/workbench/services/configurationResolver to have strict null checking.

Not all of these files are eligible to be included in the strict null build yet due to their dependencies. You do not need to fix errors outside of the configurationResolver directory

Steps

1. Add ./vs/workbench/services/configurationResolver/**/*.ts to the include section of src/tsconfig.strictNullChecks.json
2. Run yarn strict-null-check -- --watch
3. Fix strict null check compiler errors inside of the configurationResolver dir.
4. Verify normal build still works
5. Revert changes to src/tsconfig.strictNullChecks.json

[mjbvz]

Adding this to march since there are only around 30 strict null errors left in the codebase