Extracted a separate class to run dexopt on packages

performDexOptLibsLI and related methods were extracted to PackageDexOptimizer
class. Minor refactoring of PackageManagerService.

This is a non-functional change. It should simplify further work to allow
storing OAT files inside package dir.

Change-Id: I3494a2da70605362bb6fb4625ffbee1cbe1cd457