[REF] Cleanup input & output on paymentActivityCreate & improve test

[eileenmcnaughton]

Overview

Cleanup on the action that creates an activity when adding a payment

Before

Financial trxn object passed around

After

Specific variables used, more testing, api used

Technical Details

I'm trying to get away from passing around an object whose use we want to replace with an api callin the calling function

Comments

@monishdeb @mattwire

[civibot]

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[seamuslee001]

changes look fine and confirmed doing a grep that this alters all the places these functions are used, also has a test, merging

[eileenmcnaughton]

thanks @seamuslee001