MDL-40176 mock_submit method for testing

processing of data submitted from form.
MDL-40176 mock_submit changes so that

optional_param etc will work in form methods
MDL-40171 shortanswer question saving test

more tests to follow
MDL-40171 shortanswer - answer order is important
MDL-40171 test for description question type

and some small changes to shortanswer and helper
phpdoc changes
MDL-40171 multianswer qtype tests
MDL-40171 match qtype saving tests
MDL-40171 changes to tests after mock_submit

changes.
MDL-40171 tests for match question type