Expose remaining PackageState APIs for ART

- isApex temporarily while the underlying flags refactor is ongoing
- getFirstInstallTime so ART can track app use times for an LRU cache
- isOverlay to allow `isLoadableInOtherProcesses` utility, although ART
    will likely not need to worry about this flag

API-Coverage-Bug: 262593427

Bug: 256637152

Change-Id: I748f77f2edd6f6469394f6152f4429b5c92d5101