move function add_value_form_fields into base class

want to inherit the same form fields in varnumunit
update the version as we changed what is in the base class

want to be able to require these changes in base class in
child classes.
allow overriding of answers part of form in child classes

need to add units part of form in varnumunit and make some
changes to numerical answers part of form too.
move get_num_variants_in_form into base class

want to inherit in varnumunit
allow overloading of response validation by varnumunit
make grading feedback class and image work in varnumunit
separate out feedback_for_post_prefix_parts

so it can be overridden in varnumunit.
number interpreter refactored

needed to refactor as it got more complicated with the
addition of the units being graded in varnumunit.
grade fractions where not of the proper magnitude
wrote some varnumericset question walkthrough unit tests
wrote some varnumericset question walkthrough unit tests
remove thousands separator from normalised string

and minor editing of preg patterns to simplify them.
fix bug finding postfix for number
Final grade calculation was not properly applying

auto fire error penalties.
missing unit when no exp and accepting html
OU-5650 notice when removing a variable from a question
number normaliser should not remove exponent when zero
separate use of superscript and require sci notation question option
Fix codechecker issues.
Fixing fatal error caused by changes in parent class

and made answer part of form more compact.