Set com.android.gallery3d as the default system gallery

Recently, a CTS that ensured the existence of a system gallery was
added. However, this test was failing on GSI since the default holder
for the role is com.android.gallery which doesn't exist on GSI.

This change replaces the default holder with a package that exists on
all builds, including GSI and AOSP.

Test: build
Fix: 153939224
Change-Id: I4265f1d840f8c440f2e9134206893ed3fd0ea465