Disallow create_function and support PHPStan 1.12.6, getting ready for 2.0

• Add create_function as a disallowed function call (#261, thanks @BackEndTea)
• Process ClassConstFetch where $class is Name only for enums to correctly support PHPStan 1.12.6 (#266)

Internal changes:

• Add phpstan/phpstan-deprecation-rules in expectation of PHPStan 2.0 (#263)
• Fix test class name (#260, spotted by @szepeviktor, thanks)