Add SystemFeaturesMetadata to framework

Use the SDK_FEATURE_COUNT metadata field to give a tighter bound
for the system feature IPC cache. We have to first re-declare
this in PackageManager such that it's visible to other (internal)
classes where it will be used, in this case, ApplicationPackageManager.

Bug: 375000483
Test: atest PackageManagerTest
Flag: EXEMPT refactor
Change-Id: Idfd4944381f0d0e8e4f3e8ba30b37c578545fe60