As an Integrator I can use language labels in EditorPreview

[mcmietz]

As a Integrator, I can use language labels in EditorPreview, to give the editor more information about the data in contentBlock

Acceptance criteria

• In content Block Extension I could create a Backend.xlf
• I could use the label keys in EditorPreview.html

Acceptance tests

• Add an f:translate view helper with key in EditorPreview.html
• The label is shown in Backend Preview of the contentBlock

[jonaseberle]

I haven't remembered when we talked earlier, but this is why we added a EditorLLL/FrontendLLL key to the cb settings - it contains the necessary prefix (LLL: + .xlf file path + vendor + contentBlock packagename) in order to be used with LanguageService / <f:translate>:

Backend:
<f:translate key="{cb.EditorLLL}.<fieldIdentifier>.label" />

Frontend:
<f:translate key="{cb.FrontendLLL}.<fieldIdentifier>.label" />

They contain the relevant prefix even if a Default.xlf is provided instead of EditorInterface.xlf/Frontend.xlf (https://github.com/TYPO3-Initiatives/content-block-registration-api/blob/master/Classes/Service/ConfigurationService.php#L135)