libandroidfw: Improve performance of AssetManager2

AssetManager2 relied on creating a list of configurations
present in the resource table so as to avoid copying and
converting ResTable_config's from the APK on every
resource retrieval.

ResTable, however, had a better optimization that pruned
the configurations that didn't match the currently set
configuration. This vastly reduced the number of ResTable_configs
to test.

In this CL, AssetManager2 follows suite with this optimization
and only maintains the filtered ResTable_configs, falling back
to the slow path when the configuration is overridden.

Test: mma frameworks/base/libs/androidfw
Test: adb sync system data
Test: adb shell /data/benchmarktest64/libandroidfw_benchmarks/libandroidfw_benchmarks
Change-Id: Ib57b75fbb32e1d310eec146e5a12dfc6de4385f9