Make BackgroundDexOpt aware of thermal state

This change makes the BackgroundDexOpt service consider the thermal
state of the device before running.  If the device is in a moderate thermal
state or worse background dexopt will not run.

Bug: 165935246
Test: Treehugger && atest BackgroundDexOptServiceIntegrationTests
Change-Id: Ie5ccbab7aa6d414241780136407f397d326340bf