Fix Request for AvoidUnnecessaryStringBuilderCreation: false positive for non-append operations

[jborgers]

Method reverse is used on the buffer which cannot be replaced by a '+'. This validates the creation of a StringBuilder Example:

StringBuilder timestampBuilder = new StringBuilder(new SimpleDateFormat(TIME_STAMP_FORMAT).format(new Date()));
String reversedTimeStamp = timestampBuilder.reverse().append(userId).toString(); // <--- false positive

[jborgers]

There is more wrong, local var in stead of return,..Created extra unit tests.