Optimizing: Tag more arena allocations.

Replace GrowableArray with ArenaVector and tag arena
allocations with new allocation types.

As part of this, make the register allocator a bit more
efficient, doing bulk insert/erase. Some loops are now
O(n) instead of O(n^2).

Change-Id: Ifac0871ffb34b121cc0447801a2d07eefd308c14
20 files changed