feat(mount-provider): implement IPartialMountProvider

[cristianscheid]

• Resolves: feat: Implement the new partial mount provider API #2308

Summary

Implemented IPartialMountProvider in CircleMountProvider by adding getMountsForPath() and added limitToMountpoint() to CoreQueryBuilder to support filtering.

Testing

To test this implementation, I did the following:

• Temporarily commented out the if (!$this->configService->isLocalInstance($event->getOrigin())) condition in lib/FederatedItems/Files/FileShare::manage() to allow mount entries to be created locally
• Created teams mock_team_1, mock_team_2 and mock_team_3
• Created folders mock_folder_1, mock_folder_2 and mock_folder_3 and shared with their respective folders (mock_team_1, mock_team_2 and mock_team_3)
• Temporarily commented out the early return in lib/AppInfo/Application::registerMountProvider() to force registration of CircleMountProvider regardless of GlobalScale availability
• Using Xdebug with a breakpoint on circles/lib/MountManager/CircleMountProvider::getMountsForUser(), accessed nextcloud.local/index.php/apps/dashboard/, triggering the getMountsForUser() method
• Instead of running the regular method flow, I created some mock params and called getMountsForPath() directly:

$makeMountArg = function(string $path) use ($user): \OCP\Files\Config\MountProviderArgs {
	$mountInfo = new class($user, $path) implements \OCP\Files\Config\ICachedMountInfo {
		public function __construct(private \OCP\IUser $user, private string $path) {}
		public function getUser(): \OCP\IUser { return $this->user; }
		public function getMountPoint(): string { return '/' . $this->user->getUID() . '/files/' . $this->path; }
		public function getStorageId(): int { return 0; }
		public function getRootId(): int { return 0; }
		public function getMountPointNode(): ?\OCP\Files\Node { return null; }
		public function getMountId(): ?int { return null; }
		public function getRootInternalPath(): string { return ''; }
		public function getMountProvider(): string { return ''; }
		public function getKey(): string { return ''; }
	};
	return new \OCP\Files\Config\MountProviderArgs(
		$mountInfo,
		new \OC\Files\Cache\CacheEntry([])
	);
};

$this->getMountsForPath(
	'/' . $user->getUID() . '/files/mock_folder',
	false,
	[
		$makeMountArg('mock_folder_1'),
		$makeMountArg('mock_folder_2'),
		$makeMountArg('another_folder'),
	],
	$loader
);

Results

• Path filtering worked correctly when forChildren was set to false. With multiple folders on my setup (mock_team_1, mock_team_2 and mock_team_3), in the test above only the requested mounts that exist in the DB were returned for the given paths when calling getForUser() inside getMountsForPath(), confirming that limitToMountpoints() is filtering correctly at the database level.
• forChildren did not work as expected when set to true. During testing, circles always stored mountpoints relatively. For example, sharing a folder created inside mock_folder generated a circles_mount entry with mountpoint /mock_subfolder instead of /mock_folder/mock_subfolder. As a result, the LIKE '/mock_folder/%' filter used when forChildren is true will not match these entries.
• During testing, generateCircleMount() threw an exception in both the original getMountsForUser() and on new method getMountsForPath(). I believe this happened because the mount entries were artificially created by bypassing the remote instance check in FileShare::manage(), resulting in incomplete data compared to what would be present in a real GlobalScale environment.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[cristianscheid]

@provokateurin I've addressed your review comments and updated the PR description with new testing instructions. Thanks!

[cristianscheid]

@provokateurin @salmart-dev I've adjusted the PR after your suggestions. Would appreciate another review when you have a chance.