This is needed by microG GmsCore to pretend to be the official Google
Play Services package, because client apps check the package signature
to make sure it matches Google's official certificate.
FAKE_PACKAGE_SIGNATURE is declared signature|privileged so it cannot
be requested by arbitrary apps. It is auto-granted to MicroG packages
via a privapp-permissions XML shipped in vendor/pawlet.
Originally by Danny Lin <danny@kdrag0n.dev> for Android 12.
Forward-ported to Android 16 for PawletOS: logic lives in the
lock-free ComputerEngine subclass and uses the current API
(state.getFirstInstallTimeMillis() / ps.getLastUpdateTime()).
Change-Id: Ied7d6ce0b83a2d2345c3abba0429998d86494a88