Refactor ApkAsset loading APIs

To add the partner requested ResourcesProvider#loadFromDir APIs, this
change adds format type integer that allows us to reduce the number of
ApkAssets loading overrides.

This change also adds hidden offset and length based ResourcesProvider
APIs that could not make R.

Bug: 142716192
Test: atest FrameworksResourceLoaderTests
Change-Id: I926fde257cae701901dcd4ca408024feae8c90a6
Merged-In: I926fde257cae701901dcd4ca408024feae8c90a6