PROD-147: Pro-rate creditnote by quantity and allocated amount is also allocated to completed contribution line items

[olayiwola-compucorp]

Overview

In this PR, we:

• Prorate credit notes created from contributions by quantity instead of by the line-item amount.
• We ensure allocated amount is also allocated to completed contribution line items (i.e. entity financial trxn is created for completed contribution line items).

Before

The credit note is prorated by line item quantity.

After

The credit note is prorated by line item amount.

Technical Details

For the second change, where we ensure entity financial trxn is created for completed contribution line items allocation:

See here for how CiviCRM by default doesn't create entity allocate payment to completed contribution line items

However, in this PR, using the approach below, we now allocate payment to completed contribution line items

Let's consider a scenario where the contribution total amount is £200 and there are two line items:

1. Line Item 1 has a subtotal of £100.
2. Line Item 2 also has a subtotal of £100.

Suppose the user pays £200 towards the contribution and then attempts to allocate £100 to the same completed contribution. We aim to distribute this amount proportionally among the line items.

To achieve this, we utilize the following mathematical approach:

1. Calculation of Proportion:
   The proportion of the paid amount (£100) to the total contribution amount (£200) is computed as:
   $\ \text{Proportion} = \frac{\text{Paid Amount}}{\text{Total Amount}} $

2. Allocation to Line Items:
   We then use this proportion to determine the amount allocated to each line item:

   • For Line Item 1: $\ \text{LineItem1[amount]} = \text{Proportion} \times \text{LineItem1[Subtotal]} $
   • For Line Item 2: $\ \text{LineItem2[amount]} = \text{Proportion} \times \text{LineItem2[Subtotal]} $

[jamienovick]

@olayiwola-compucorp could we submit this as a pr to core? I think this is actually a core bug so I think we could patch it directly but maybe you / @omarabuhussein / @erawat feel differently?

[olayiwola-compucorp]

PR to correct line item payment calculation submitted to core civicrm/civicrm-core#29350

This PR now contains credit note specific changes @erawat