Stop using mtNone as marker for CHeap allocations in GrowableArray

Today we use mtNone to denote that a GrowableArray should *NOT* be backed by a CHeap allocated array.

I've gotten feedback that it would probably be good to limit the usage of mtNone, and at some point maybe completely remove it.

This patch takes a small step to remove mtNone from the GrowableArray. What's left is only asserts to forbid that value. Those asserts will be trivial to remove when/if mtNone is removed.

Just like in the proposed patch to make MEMFLAGS non-optional in CHeapBitMap (see JDK-JDK-8296774), I have thrown around the parameter order for GrowableArray. When looking at the changes to the usages of CHeap-backed GrowableArrays it becomes apparent that all of these usages where forced to provide a value for the initial capacity. When MEMFLAGS move to the front, we can now skip having to figure an initial capacity.