[Translation] TranslatorBag::diff now iterates over catalogue domains instead of operation domains

[welcoMattic]

Q	A
Branch?	5.4
Bug fix?	yes
New feature?	no
Deprecations?	no
Tickets	Fix #47886
License	MIT
Doc PR

For Loco Provider (at least, but I'm pretty sure it applies for Lokalise and Crowdin), the --force option on translation:push command has no effect.

The main cause is located in the TranslatorBag::diff method which was iterating over $operation->getDomains() to add new messages to the diff catalogue. But, the fact is $operation->getDomains() returns all domains AND their +intl-icu variants! Which is certainly not what we want here.

See the test that covers the case

public function testDiffWithIntlDomain()
{
    $catalogueA = new MessageCatalogue('en', [
        'domain1+intl-icu' => ['foo' => 'foo', 'bar' => 'bar'],
        'domain2' => ['baz' => 'baz', 'qux' => 'qux'],
    ]);

    $bagA = new TranslatorBag();
    $bagA->addCatalogue($catalogueA);

    $catalogueB = new MessageCatalogue('en', [
        'domain1' => ['foo' => 'foo'],
        'domain2' => ['baz' => 'baz', 'corge' => 'corge'],
    ]);

    $bagB = new TranslatorBag();
    $bagB->addCatalogue($catalogueB);

    $bagResult = $bagA->diff($bagB);

    $this->assertEquals([
        'en' => [
            'domain1' => ['bar' => 'bar'],
            'domain2' => ['qux' => 'qux'],
        ],
    ], $this->getAllMessagesFromTranslatorBag($bagResult));
}

Without the change, 'foo' => 'foo' was in the result bag.

Replaces #47986

[fabpot]

Thank you @welcoMattic.