Function createFakeSettings

createFakeSettings(): FakeSettings
Creates a fake settings capability.

Implements VS Code's documented resolution rather than a convenient approximation: the supported tiers apply in VS Code precedence order, a language value outranks a more local non-language value, and only object values merge (shallow) while everything else is overridden outright. The same contract suite runs against this and the real adapter for the port contract. Platform configuration behavior not exposed by the port remains an Extension Host concern.

Returns FakeSettings
Example
```
const settings = createFakeSettings();
settings._set('sample.projects', 'enabled', 'globalValue', false);
settings._set('sample.projects', 'enabled', 'globalLanguageValue', true, {
  languageId: 'typescript',
});
```
- Defined in src/testing/fakes/fake-settings.ts:112