Use session id to uniquely identidy autofill ids for multi-session.

This change is need when integrating CustomDescription artifacts (like
CharSequenceTransformation) with SaveInfo.FLAG_DELAY_SAVE, as different
views might have the same autofill id on different activities.

Test: atest CtsAutoFillServiceTestCases:MultiScreenLoginTest
Test: atest CtsAutoFillServiceTestCases # to make sure it didn't break anything

Fixes: 113593220

Change-Id: I7db1df7a56dec7180a2172bb2022b042f115c7b8