[Autofill Frameowork] Refactor get save info stats function into

autofill.Helper class

Follow up CL per comment in ag/27285239

Bug: b/338600483
Test: atest CtsAutoFillServiceTestCases &&
      atest FrameworksServicesTests:HelperTest

Change-Id: If134e425fcdb2a1ddc288eb5b3e846b9e86f9a7b