Allow dynamically choosing the MEMFLAGS of a type without ResourceObj

CHeapObj currently requires a template to specify which flags an object should be allocated with. This makes sense for most objects, but not utilities like GrowableArray our outputStream.

Instead these classes must, unnecessarily, be ResourceObjs.

Suggest a third way of doing things, without the cost of ResourceObjs (24 bytes of allocated space for each instance, for example).