Reroute to Credman based on autofill hint

Currently, Autofill Manager looks at the view's isCredential attribute
to suppress fill dialog. Add a new autofill hint that Autofill Manager will look at to regard in the
same manner as the isCredential attribute. This hint will be set by the
Credential Manager's support library.

The autofill hint has been available for older Android versions while
isCredential is only available for U+. In the future, if AwG can support
rerouting to CredentialManager based on the autofill hint, we could
enable Credman support in Autofill for U-.

Bug: 299319802
Test: atest CtsAutoFillServiceTestCases
Change-Id: I157735334c4141a78f5743282dd09c32e3200e6a