[TASK] Restructure functional frontend tests

In the scope of enabling Extbase frontend rendering during
functional test runs, the response object contains multiple
data values for TypoScript ("default") and the called Extbase
actions. Processing them all at once just has practical reasons
to avoid additional frontend requests for each aspect.
To decouple the actual testing structure from assertions
and constraints, a new Contraint namespace has been introduced.

The irre_tutorial extension has been enriched with an accordant
frontend rendering for Extbase context to return structured JSON
data like in the current frontend tests.

This change contains Extbase TypoScript which will be activated
in a separate bugfixing change.

Resolves: #59521
Releases: 6.2
Change-Id: I42c0bf8957d9c4c1e4389049695512851b436d14