[Autofill] Move ShouldBeParsed() & friends out of FormStructure (1/2)

This CL is one of two CLs that move the implementations of
- FormStructure::ShouldBeParsed()
- FormStructure::ShouldRunHeuristics()
- FormStructure::ShouldRunHeuristicsForSingleFields()
- FormStructure::ShouldBeQueried()
- FormStructure::ShouldBeUploaded()
- FormStructure::ShouldUploadUkm()
- FormStructure::IsAutofillable()
to free functions. The member functions will forward to these free
functions.

See crrev.com/c/6917895 for the larger motivation of this change.

This CL's sole purpose is to present a reviewable diff of the old
member functions and the new free functions.

The followup CL moves the new free functions to a separate file.

Bug: 427787155, 40232021
Change-Id: Ide951718d734137604392c0c4dacb3ebafc1d805
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6918214
Commit-Queue: Christoph Schwering <schwering@google.com>
Reviewed-by: Jan Keitel <jkeitel@google.com>
Cr-Commit-Position: refs/heads/main@{#1511410}