ContentTranslationContextualLinksTest should use API to set up language

Problem/Motivation

ContactLanguageTest uses a form submission to change language settings.

This is expensive, and not what the test should be covering. The comment says:

    // Use a UI form submission to make the node type and field translatable.
    // This tests that caches are properly invalidated.

but:

1. If this is actually being tested, it's in the wrong test class - ContentTranslation**ContextualLinks**Test shouldn't be covering something as basic as cache clearing in the UI.
2. I suspect that it's actually a mistake in the comment, and that what is meant is 'Using the UI *ensures* that caches are invalidated'.

Steps to reproduce

Proposed resolution

Change to an API call.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet