Provide a way to set AutofillId on ViewStructure.

So far that was done indirectly by public methods that could
be overridden in away that does not set the proper id in the structure,
which would crash apps.

Bug: 36171235
Test: modified VirtualContainerActivityTest#testAutofillOverrideDispatchprovideAutofillStructure

Change-Id: I3f1c64020125cbb8349971a0bc52ccd1e0c81e62