[REF+ test] start process of cleaning up payment activity handling

[eileenmcnaughton]

Overview

Minor readability cleanup + test extension

Before

Less readable, less test cover

After

More readable, more test cover

Technical Details

At the moment activities are created when using the additional payment form but not the UI.
This needs cleaning up & this takes the first step by adding testing & slightly
simplifying where decisions are made about variables (assign title directly rather than component
just to assign title deeper down

Comments

[civibot]

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[eileenmcnaughton]

test this please