Call apiv4 from Contribution create rather than fugly addActivity function

Call apiv4 from Contribution create rather than fugly addActivity function

I took a look at https://github.com/civicrm/civicrm-core/pull/17274 which has blocking test failures - but felt that
the shared function was adding nothing and simply using the api to create the activity made more sense. The
shared function does a lot of silly wrangling for very little shared functionality and is
hard to read. In this call only 2 params are passed in - so most of the wranglingg
doesn't apply anyway. I ensured the 2 JIRA issues referenced in the removed code have test cover (one already
had a test written by Monish & I added in the campaign check