Raise PHPStan level to 9

[IanDelMar]

• (Not related to level 9) Requires functionMap.php in the constructor. We hardly gain anything by doing this in getAdditionalTagsFromMap(). Adds a doc comment to inform PHPStan of the type change after array_shift().
• Renames $name to $fullSymbolName to indicate what name the variable holds throughout the method. Adds a doc comment to $fullSymbolName to let PHPStan know about its type.
• Replaces a check for the existence of the stmts property with checks for ClassLike and Namespace_ entities. This helps PHPStan understand what to expect from $node->stmts. Only ClassLike and Namespace_ need their children to be traversed.

[szepeviktor]

Thank you.