Make getCallingUidOrThrow() not throw in clearCallingIdentity() blocks

The new method hasExplicitIdentity will track whether the caller is
within a Binder.clearCallingIdentity/restoreCallingIdentity block based
on packing this state information into the token returned by clearCallingIdentity.

Bug: b/252975769
Test: android.os.cts.BinderTest
Change-Id: I162db933f9e52cd6f9f46796bda11ad6216d3d66