IBX-11437: Implemented reference aware external storage

[barw4]

🎫 Issue	IBX-11437

Related PRs:

ibexa/admin-ui#1856
https://github.com/ibexa/fieldtype-page/pull/191
https://github.com/ibexa/installer/pull/207

Description:

Problem

When creating a new content version (draft), all field external storage data is fully copied for every translation — even translations not being edited. For field types with complex external storage (e.g. Page Builder with zones, blocks, attributes across multiple tables), this causes thousands of redundant queries per draft creation.

Solution

A new ReferenceAwareExternalStorage interface allows field types to opt out of copying external data for untouched translations during draft creation. Instead of duplicating data, the storage creates a lightweight reference to the source version's data and resolves it transparently on read.

interface ReferenceAwareExternalStorage
{
    public function referenceLegacyField(
        VersionInfo $versionInfo,
        Field $field,
        Field $originalField
    ): ?bool;
}

For QA:

Documentation:

[alongosz]

@barw4 nitpick: could you please fix PRs titles so they include a verb per internal conventions? e.g. "Implemented" - ideally in past simple so we don't forget to change it in the merge commit.

More interesting remarks:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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