IBX-4477: Added LocationService::getSubtreeSize method

[adamwojs]

Question	Answer
JIRA issue	IBX-4477
Required by	ezsystems/ezplatform-admin-ui#2085
Type	bug
Target Ibexa version	v3.3
BC breaks	no
Regression build	ibexa/commerce#214

Added dedicated method to retrieve subtree size

interface LocationService {
    # ...

    /**
     * Return the subtree size of a given location.
     *
     * Warning! This method is not permission aware by design.
     */
    public function getSubtreeSize(Location $location): int;

    # ...
}

Checklist:

• Provided PR description.
• Tested the solution manually.
• Provided automated test coverage.
• Checked that target branch is set correctly (master for features, the oldest supported for bugs).
• Ran PHP CS Fixer for new PHP code (use $ composer fix-cs).
• Asked for a review (ping @ezsystems/engineering-team).

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[micszo]

With customer's DB locally observed very significant performance improvement. 💪🏻

QA Approved on Ibexa Experience 3.3.31-dev.

Side, also noticed that now copy subtree (except -1 / no limit) is disabled for a one element tree. Before it was possible to use copy subtree as copy.