Cache null binder results in PIC

PropertyInvalidatedCache treated a null binder result as a cache miss.
This changes that behavior to always cache a null result as a normal
result.  This also provides an override so that individual caches can
revert to legacy behavior.  A new counter is part of dumpsys cacheinfo
that reports the number of null binder results.

Flag: android.app.pic_cache_nulls
Bug: 378762206
Bug: 372923336
Test: atest
 * FrameworksCoreTests:PropertyInvalidatedCacheTests
 * FrameworksCoreTests:IpcDataCacheTest
 * CtsOsTestCases:IpcDataCacheTest
Change-Id: Ia8e102600b59b61b435b258559803a8d8518368d