Fix post-filling logic in the renderer

This CL fixes two problems:

- AutofillAgent::ApplyFieldsAction() uses FormFieldData::host_form_id in
  order to get the owning forms of fields, whereas this information is
  populated before the filling operation and many other operations that
  can trigger JS happen, meaning that this information is not
  necessarily accurate (and is probably one cause of some crashes)

- The method also uses `fields` and `filled_fields_ids` inconsistently.
  `fields` shouldn't be used after calling
  `form_util::ApplyFieldsAction()` because it is not representative of
  what fields were actually filled.

The CL fixes this by introducing a map `filled_fields_and_forms ` that maps each "filled" field to its actual updated owning form. and it uses
this map everywhere after calling the filling function.

Note that this makes `FormFieldFata::FillData::host_form_id_` obsolete
but the CL doesn't remove it since it has some iOS references.

Bug: 40947729, 392907891
Change-Id: I069bcc5f42747381c86de6898f0d8e2db8b0eee5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6218588
Reviewed-by: Christoph Schwering <schwering@google.com>
Commit-Queue: Jihad Hanna <jihadghanna@google.com>
Cr-Commit-Position: refs/heads/main@{#1418081}