Disallow partial uses in ReferenceUsedNamesOnly

[dereuromark]

Partial namespace references like Mockery\MockInterface (as opposed to FQCN \Mockery\MockInterface) were not flagged by SlevomatCodingStandard.Namespaces.ReferenceUsedNamesOnly because Slevomat's allowPartialUses property defaults to true. Setting it to false makes the sniff flag such references so they must be imported via a use statement.

Related: cakephp/cakephp-codesniffer#430 — same bug confirmed in this ruleset.

Before

namespace App\Test;

class FooTest {
    public function bar(Mockery\MockInterface $x): void {}  // not flagged
}

After

ERROR | Partial use statements are not allowed, but referencing Mockery\MockInterface found.

The FQCN form (\Mockery\MockInterface) was and remains flagged by the same sniff via ReferenceViaFullyQualifiedName.

Note: this is a behavior-tightening change. Downstream code that intentionally uses partial imports (e.g. use Doctrine\ORM\Mapping as ORM; + ORM\Entity) will now error.