[META] Deprecate non-static random generation methods from RandomGeneratorTrait

At first glance, this might become a META where we deprecate methods one by one, since especially $this->randomMachineName() is used a _lot_, but let's see where we end up if we go all in.

To be honest, I'm not even sure this is worth doing. Having a trait in the base classes and calling the methods non-statically allows avoiding the use import.

Hmm, that makes sense, we're looking at ~2500 lines of changed code here.

Maybe we do a nice "Closed (won't fix)" and move on to bigger (or rather smaller in code lines) and better things?

Maybe we could limit to deprecating the use of the magic __gets introduced by the parent (i.e. stop allowing accessing the property directly) and maybe RandomGeneratorTrait::randomStringValidate() which is just a callback that is no longer called since the entire implementation moved to the new static methods.

The __get was the one from the original issue that I thought we might not want to keep around forever.

$this->randomMachineName() seems like it might be more trouble than it's worth to get rid of.

There are also \Drupal\Tests\UnitTestCase::randomMachineName and\Drupal\Tests\UnitTestCase::getRandomGenerator that are now basically copies of the methods in the Trait.

Do we want/need to do anything with those?

Maybe in UnitTestCase we could use the trait and remove the direct implementations?

Opened 🐛 Fix incorrect usage of randomStringValidate in \Drupal\Tests\jsonapi\Kernel\Normalizer\JsonApiDocumentTopLevelNormalizerTest::setUp Fixed about some weird/incorrect usage of RandomGeneratorTrait::randomStringValidate()

Turned this issue into a META to prevent child-issues from delaying up each other from being committed.