Forms: fix unclicking standalone form buttons

We can find pdf forms that eg. have three related
radio buttons where their *only* relationship is
having the same full qualified name.

Such a form is supported by Adobe Reader and
produced by LaTeX through TeXStudio. So, when
clicking one such radio button, Poppler failed
to unclick the other radio buttons as they are
not children nor parent of the clicked one (which
is the ordinary way to set radio button groups
as per the PDF standard).

So, when clicking a radio button, let's add support
to find other radio buttons in the same page that
are only related by having same fully qualified name
(these may be in standalone or normal fields).

Where trying to find where PDF standard covers this
special case of related radio buttons, the closest
thing we can find is section "Field names" inside
chapter "8.6.2 Field Dictionaries" in 1.7 PDF spec.

Issue #1034
7 jobs for radio_standalone in 5 minutes and 43 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #8365544
build

00:05:20

passed #8365549
build_android

00:01:02

passed #8365545
build_clang_libcpp

00:05:43

passed #8365548
build_clazy

00:03:04

passed #8365547
build_mingw64_fedora

00:04:01

passed #8365546
build_ubuntu_18_04

00:02:47

passed #8365543
clang_format

00:01:23