[Autofill] Migrate TypeGroupToFormType() calls to GetFormTypes()

This CL migrates expressions using FieldTypeGroupToFormType() to
GetFormTypes().

This CL is a no-op because all existing AutofillTypes only hold a
singleton FieldTypeSet and therefore GetFormTypes().size() <= 1.

Bug: 432645177
Change-Id: I4fefdd87aab62d8849d83df7058a8c4b6fd69aa8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6802080
Reviewed-by: Dominic Battré <battre@chromium.org>
Reviewed-by: Jan Keitel <jkeitel@google.com>
Commit-Queue: Christoph Schwering <schwering@google.com>
Cr-Commit-Position: refs/heads/main@{#1495630}