watchedFiles fails to watch nested files on linux

## Problem

recursive file watching doesn't work on linux since vscode 1.67 ...?

this test fails:

```
1) CloudFormation Template Registry
adds dynamically-added template files with yaml and yml extensions at various nesting levels:
Error: Timed out waiting for registry to populate. Actual item count: 1. Expected item count: 2.
```

comparing logs shows that we don't get an event for the nested file:

```diff
- CloudFormationTemplateRegistry: manager detected a new file: .../src/testFixtures/workspaceFolder/1/nested/test.yaml
CloudFormationTemplateRegistry: manager detected a new file: .../src/testFixtures/workspaceFolder/1/test.yml
```

- https://github.com/aws/aws-toolkit-vscode/pull/2622#issuecomment-1120001687

## Solution

1. find root cause
2. report upstream?

related? https://github.com/microsoft/vscode/issues/148245

Start by reproducing the failing CloudFormation Template Registry test and compare watcher logs for the nested and top-level files. Inspect the watchedFiles behavior, then review the linked VS Code issue and PR comment for the Linux regression context. Done means identifying the root cause and either reporting it upstream or documenting the resulting fix.

Written by the indexing model from the issue text.