feat: phpDoc to property/return/param Fixer - allow fixing mixed on PHP >= 8

[MortalFlesh]

Hello,

I'm trying to use PhpdocTo Property/Return/Param Fixers for fixing a mixed type from phpdocs on PHP >= 8.0 - which allows mixed as a declared scalar type.

It seems to me, it should work. But it is actually skipped before even trying to check if the type is allowed for the version.

I removed the mixed from a skipped types and it is checked against a version specific types later, so it works fine.
I also unified test cases for all 3 fixers, so it lowers a brain damage for managing the tests.

PS:
I created the PR from master and marked it as a feature not as a bugfix, since I feel it as an improvement in the fixing - not fixing a bug, but I can change it if it should be a bugfix.

[coveralls]

Coverage decreased (-0.0008%) to 92.836% when pulling 67c1ff1 on MortalFlesh:feature/fix-mixed-in-phpdocs into 17e5591 on FriendsOfPHP:master.

[julienfalque]

The description of those fixers are outdated, they say:

• they only fix "non-mixed types"
• they require an old PHP version

Can you update them please?

[keradus]

@MortalFlesh , would you mind to address julienfalque's comments, so we can merge this great PR?

[MortalFlesh]

Hello @keradus I will try to do it today, I'm kinda busy these days :)

[Wirone]

@MortalFlesh is it possible to rebase this PR, so we can check current pipeline result and continue the review process?

[coveralls]

coverage: 94.604%. remained the same when pulling 4305639 on MortalFlesh:feature/fix-mixed-in-phpdocs into 5f102b4 on PHP-CS-Fixer:master.

[Wirone]

We need to clean this up a little 😉.

[Wirone]

Thank you @MortalFlesh 🍻