Record data about dex files use on disk

Add DexManager to keep track of how dex files are used.

Every time a dex file is loaded, PackageManager will notify DexManager
which will process the load. The DexManager will look up what package
owns the dex file and record its use in package-dex-usage.list (through
PackageDexUsage).

Test: device boots, package-dex-usage.list is created and contains valid data, after device reboot the list is succesfully read from disk.
runtest -x .../PackageDexUsageTests.java
runtest -x .../DexManagerTests.java

Bug: 32871170
Change-Id: If5496c3b95820b537260c326d4eaa04eb50b1d8c