Sets AutofillClient on attachBaseContext()

When an activity overrides attachBaseContext(), the attached context must share
the same AutofillCient, otherwise it will break autofill in the activity.

Test: cts-tradefed run commandAndExit cts-dev -m CtsAutoFillServiceTestCases -t android.autofillservice.cts.AttachedContextActivityTest
Test: cts-tradefed run commandAndExit cts-dev -m CtsAutoFillServiceTestCases

Fixes: 67350639

Change-Id: I6b0c4c2fab5fa68eb6ee0714e107ca0816efb2cb