GC triggering performance optimizations

Copy the correct starting heap size at process init.
Interfaces to set GC/managed heap parameters.

Change-Id: I3f3f60915e0c732436118e8e605393360c89bfe4
(cherry picked from commit a6f2e5f1162760178b8cb412c6beee6a5cbce429)
(cherry picked from commit fe9675349c1c0fe2a92e7cb2d9b8bd830f225103)
(cherry picked from commit be6f88153d8e515d9decf4274efdc5f76c87e2b9)