Issue #3516147 by dydave: PHPSTAN: Raised validation level from 0 (min) to 9 (max).

https://www.drupal.org/project/image_link_formatter/issues/3516147

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

Fixed all validation errors, mostly:

• Updated Doc comment blocks return types.
• Updated Doc comment blocks param types.
• Added inline @var types definitions.
• Changed a single line of code, to add a null coalescing operator.

merged