Expose isInstantApp() to more callers

Instead of just allowing the instant app itself, also allow anyone
with ACCESS_INSTANT_APP permission or apps that the instant app
has granted access.

Change-Id: I5a79ef9520db908ba9ab56af0157b1646d2d8cc1
Fixes: 34123112
Test: cts-tradefed run commandAndExit cts-dev -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.EphemeralTest