Hide files excluded with files.exclude from Project Panel

The project panel should respect the `files.exclude` VS Code setting.
This setting is combined with the existing
`swift.excludePathsFromPackageDependencies`.

The tests required an update to `updateSettings`, as the existing global
`files.exclude` settings are combined with the ones set in the test.
When setting the settings, verify that all expected settings are present
before continuing, but don't require the settings object to be an exact
match of what we set.

Author: plemarquand