[BUGFIX] Use native phpunit functionality in Fluid tests

Some "methods" used in ViewHelpers to mock a class (RenderingContext)
which only uses a fixture to avoid constructor calls
can be achieved by using phpunit's getMockBuilder() logic
itself, making this class in the testing framework
useless. TYPO3 Core should not depend on this,
but rather use native phpunit logic.

Some other things are moved to the specific classes
where they are needed, so setUp() will be much faster
for other ViewHelper test classes.

Resolves: #89793
Releases: master
Change-Id: Ia2b2d9e3d4a7bd9a6eabd254259ff24ff3565e65
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62451


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>