Add more details to subscription update activity

[ejegg]

Overview

Adds info about changes in the cycle day or next scheduled contribution date to the activity created when editing a recurring contribution.

Before

If you edit the cycle day and the next scheduled contribution date of a recurring contribution they are not mentioned in the edit activity.

After

If you edit the cycle day and the next scheduled contribution date of a recurring contribution the old and new values are mentioned in the edit activity, e.g.:

Cycle day has been updated from 1 to 16 for this subscription.
Next scheduled contribution date has been updated from to 2024-02-16 for this subscription.

Technical Details

Includes a couple of small cleanup patches

dev/core#5008

[civibot]

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[eileenmcnaughton]

@ejegg style ^^

[mattwire]

Thanks @ejegg we talked about this at the sprint in Montreal. It was felt that either (1) we should not record an activity at all. or (2) more information is always useful.

Because this is just extending existing code by extracting into it's own function I am happy to see this added so I have merged it.