[BUGFIX] Stop mocking classes that do not exist

This is only possible with PHPUnit, not with Prophecy, and it is bad
practice as there is no way to do type analysis on classes that do
not exist.

Also avoid using mocks where an `stdClass` instance does just fine.

Used command:
> ./Build/Scripts/runTests.sh -s phpstanGenerateBaseline

Resolves: #97634
Releases: main, 11.5
Change-Id: I2a92678a60df7bd762688e3b7571b18f861340d9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74621


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>