[Autofill] Move FormFieldData::section_ to AutofillField

This CL moves the `Section` member from FormFieldData in core/common
to AutofillField in core/browser.

That's necessary because we'll determine FillingProduct- and perhaps
even EntityType-specific Sections. The necessary types aren't visible
in core/common.

As a result, this CL moves and deletes quite bit of code and includes
one ugly hack:

- Good: It moves the class Section to autofill_field.h.
- Good: It moves FormFieldData::section_ to AutofillField::section_.
- Good: It deletes FormFieldData::FillData::section.
- Good: It deletes all the Mojo code for Sections.
- Bad: It adds a hacky Section parameter to
  AutofillDriver::ApplyFormAction(). This parameter is only needed for
  and used by iOS. The reason is that Bling still implements "Clear
  Form" rather than "Undo Autofill", and "Clear Form" resets all fields
  of in the same section as the trigger field. To this end, on iOS, the
  renderer still needs to know which section the filled fields belong
  to. This parameter has an appropriately bulky name. It can be deleted
  when Bling replaces "Clear Form" with "Undo Autofill".

Bug: 430871528, 40232021
Change-Id: I447b5a11390f060fdb6654db3db6efec5eb6fb78
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6725674
Reviewed-by: Vincent Boisselle <vincb@google.com>
Reviewed-by: Antonio Sartori <antoniosartori@chromium.org>
Reviewed-by: Jihad Hanna <jihadghanna@google.com>
Commit-Queue: Christoph Schwering <schwering@google.com>
Reviewed-by: Jan Keitel <jkeitel@google.com>
Cr-Commit-Position: refs/heads/main@{#1486270}