Shenandoah should allow arbitrarily low initial heap size

Shenandoah heap regions checks verify that initial heap size covers at least 10 regions. This means the lowest uncommitted size is at least 10*RegionSize, which is a lot for large heaps. This seems to be the reminiscent of old resizing scheme, where Shenandoah could have run with "initial heap" for a long time, before GC code decided to resize. There is little sense it in now: Shenandoah would commit regions up to max_capacity if needed, including during the initial barrage of allocations. We should instead check that "max" heap size covers at least 10 regions.