Move the invocation rate limiter class out of helpers.ts

[robertbrignull]

Moves the InvocationRateLimiter class out of helpers.ts and into its own file. Then by having it take the Memento interface as an argument instead of the full ExtensionContext we can move it to the common directory and dramatically reduce the amount of mocking in the tests.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[robertbrignull]

I'm not hugely happy that we're doing as any in the tests, but I don't think the change in this PR makes it any worse than it was already.

[koesie10]

Thanks for moving this!

[koesie10]

I see that this is from the previous testing implementation, but do we need this? It seems like just having MockMemento is enough.

[robertbrignull]

Ah, I see why we had this. It's because the real type defined on the ExtensionContext is

readonly globalState: Memento & {
	/**
	 * Set the keys whose values should be synchronized across devices when synchronizing user-data
	 * like configuration, extensions, and mementos.
	 *
	 * Note that this function defines the whole set of keys whose values are synchronized:
	 *  - calling it with an empty array stops synchronization for this memento
	 *  - calling it with a non-empty array replaces all keys whose values are synchronized
	 *
	 * For any given set of keys this function needs to be called only once but there is no harm in
	 * repeatedly calling it.
	 *
	 * @param keys The set of keys whose values are synced.
	 */
	setKeysForSync(keys: readonly string[]): void;
};

So we had to implement setKeysForSync too. But now we've declared that InvocationRateLimiter only takes a Memento instead of typeof ExtensionContext.globalState, we don't have to mock this method in the tests anymore.