Adds Contextual Search calling package name.

This is mostly useful for the self-invocation API, so the
designated ContextualSearch app can see which app invoked them.

Bug: 368653769
Test: Build and flash, invoke with SupportApp
Flag: android.app.contextualsearch.flags.self_invocation
Change-Id: I41c111f540c9f93c3bc989014faef8c5024090a0