Credential Autofill Service integration

Current impl (Patchset 3) solves the following scenarios:

1. Credman only screen.
2. Autofill only screen.
3. Mixed screen, meaning the assistStructure contains both credential and autofill fields.

It does not solve the following scenario perfectly.

1. When the user goes from credman screen to autofill screen, and autofill manager decides to reuse the same session.

-> Autofill Provider will reuse the old assistStructure and fail to receive a fill response that contains the new screen.
-> Credman Provider will request a new assistStructure and a new fill response because a view that is not tracked has entered.
-> Credman Provider will return an error saying the assistStructure does not contain a viewNode that is credential.
-> Session will get destroyed and recreated with Autofill Provider being the primary provider.
-> Session returns autofill suggestions for the autofill screen.

This results in eventual availability but the user will have to jump between fields two times before it comes available. This will be addressed in the follow-up cl that will have each autofill provider maintain its own assist structure.

Test: atest CtsAttentionServiceDeviceTestCases, atest CtsAutoFillServiceTestCases:android.autofillservice.cts.inline.InlineLoginMixedCredentialActivityTest
Bug: 307413215
Change-Id: Ib9eb48ff6729d6c14960f4995d794849f02d9d35