Fixed splitStrings and stringArray breaking a quoted constructor class key - #1466

class A { 'constructor'() {} } is a real constructor, but with splitStrings or stringArray the key got rewritten in place into 'co'+'ns'+... or a string array call while staying a non-computed key, so the output didn't parse. ClassFieldTransformer already leaves constructor as a plain literal on purpose (a computed key would stop being the constructor), the shared isProhibitedLiteralNode guard just didn't know about class keys. Extended it to non-computed MethodDefinition/PropertyDefinition keys, the same rule it already applies to object Property keys. Other quoted keys are made computed before the string transforms run, so they are still split/arrayed as before.

The two existing stringArray expectations in ClassFieldTransformer.spec.ts listed constructor in the string array, which was the bug, so they now match the identifier-key variant and bar moves from index 0x2 to 0x1. New unit cases for MethodDefinition/PropertyDefinition keys and a splitStrings variant on the literal-key fixture fail on master.

Fixed #1464