white lists getter and setter acceseors for having stage-2 decorators (#766)

- adds `get` and `set` kind in addition to `method` to the list of allowed class members for having a decorator,
- adds tests for this two cases (decorator + set and decorator + get)

src/parser/statement.js

@@ -899,7 +899,7 @@ export default class StatementParser extends ExpressionParser {
 
       if (
         this.hasPlugin("decorators2") &&
-        member.kind != "method" &&
+        ["method", "get", "set"].indexOf(member.kind) === -1 &&
         member.decorators &&
         member.decorators.length > 0
       ) {