Allocate dex cache arrays at startup.

And deallocate them post startup.

Local measurements for app startup average of 1000 runs
on Pixel 5 and master:
- youtube: 1035 -> 985
- maps: 1142 -> 877

Test: test.py
Change-Id: I4fb6e7e2cecdea8bf977ef3b59d47efd0b8b9b74