PHPSTAN: Raise validation level from 0 (min) to 9 (max)

Quick follow-up on this issue:

Starting from level 3, I gradually raised the level and each time fixed all the errors prompted by PHPSTAN, until reaching level 9.

Fixed all validation errors, mostly:

• Updated Doc comment blocks return types.
• Updated Doc comment blocks param types.
• Added inline @var types definitions.

 
Only a single line of code was changed, to add a null coalescing operator:
https://git.drupalcode.org/project/image_link_formatter/-/commit/58e55af...

Since the Tests of the MR all passed 🟢, I went ahead and merged the changes above at #3.

The configuration change was made on Gitlab CI by adding the file: phpstan.neon, forcing rule level to 9.

This should be helpful keeping module's code properly maintained with the evolution of the different Core versions, APIs and PHP versions.

Marking issue as Fixed for now.

Thanks!

Automatically closed - issue fixed for 2 weeks with no activity.