IBX-12530: Added SchemaApplier for executing a built Schema against a connection

[Steveb-p]

🎫 Issue	IBX-12530

Related PRs:

• https://github.com/ibexa/core/pull/PLACEHOLDER_CORE — consumer; IbexaKernelTestTrait::loadSchema()
• https://github.com/ibexa/test-core/pull/PLACEHOLDER_TC — consumer; DatabaseSchemaHook

Description:

SchemaBuilderInterface produces a Schema but has no way of putting it into a database, so every
caller reimplements the same toSql()-and-execute loop. There are already two, and they differ in
one detail:

• ibexa/test-core's DatabaseSchemaHook — runs once per suite against a freshly created database,
  so a plain create is enough.
• ibexa/core's LegacySchemaImporter — runs per test case from IbexaKernelTestTrait::loadSchema(),
  so it drops the schema's tables first (in reverse order, for FKs) and recreates them.

SchemaApplier covers both, with $dropExistingTables selecting between them. It lives here
because this package owns SchemaBuilder, and because it is the only place both consumers can
reach: ibexa/core cannot depend on ibexa/test-core (the dependency runs the other way), and both
already require ibexa/doctrine-schema — core in require, test-core in require-dev.

public function applySchema(Schema $schema, bool $dropExistingTables = false): void;

Registered as Ibexa\Contracts\DoctrineSchema\Builder\SchemaApplierInterface, alongside the
existing SchemaBuilderInterface alias.

Nothing existing changes behaviour — this is purely additive; the two consumers switch over in
their own PRs.

For QA:

composer test — 32 tests / 31 assertions / 4 skipped, unchanged apart from the 4 new ones.
PHPStan and code style clean.

The new SchemaApplierTest covers the behaviour that matters, against in-memory SQLite: a plain
apply creates the tables; applying twice without dropping fails; applying twice with dropping
succeeds and leaves the table empty (proving it really was dropped and recreated, not just
tolerated); and dropping is skipped for tables that do not exist yet.

[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

See analysis details on SonarQube Cloud