Add hash set

More memory efficient than libcxx since we do not box the values.

Change intern table to use new hash set. Clean up intern table by
removing const casts and deleting unnecessary code.

Changed the class linker to use a hash set, also added a pre-zygote
class table.

5 samples of:
adb shell stop && adb shell start && sleep 60 && adb shell dumpsys meminfo
Before:
165929 kB: Native
175859 kB: Native
168434 kB: Native
166559 kB: Native
169958 kB: Native

After:
160972 kB: Native
159439 kB: Native
157204 kB: Native
165093 kB: Native
163039 kB: Native

TODO: Add HashTable which is implemented by using a HashSet.
TODO: Use for DexFile::find_class_def_misses_.
TODO: Investigate using mem maps instead of native heap.

Bug: 17808975

Change-Id: I93e376cf6eb9628cf52f4aefdadb6157acfb799a

(cherry picked from commit e05d1d5f)