Use ScopedArenaAllocator for code generation.

Reuse the memory previously allocated on the ArenaStack by
optimization passes.

This CL handles only the architecture-independent codegen
and slow paths, architecture-dependent codegen allocations
shall be moved to the ScopedArenaAllocator in a follow-up.

Memory needed to compile the two most expensive methods for
aosp_angler-userdebug boot image:
  BatteryStats.dumpCheckinLocked() : 19.6MiB -> 18.5MiB (-1189KiB)
  BatteryStats.dumpLocked(): 39.3MiB -> 37.0MiB (-2379KiB)

Also move definitions of functions that use bit_vector-inl.h
from bit_vector.h also to bit_vector-inl.h .

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 64312607
Change-Id: I84688c3a5a95bf90f56bd3a150bc31fedc95f29c