Fix double loop on lineItems

[eileenmcnaughton]

Overview

Removes unwanted complexity from code

Before

Calling

civicrm_api3('Payment', 'create', ['total_amount' => 500])

passes through different code than

civicrm_api3('Payment', 'create', ['total_amount' => 500, 'line_item' => [[4 => 50], [10 => 450]])

After

Information from the line_item array is 'lifted' early on and then the same loop is used.

Technical Details

Historically the code followed 2 loops - one for the (very rare) situation when an array of
'line_item' was passed in - in fact this array is an array of arrays where each array represents
the id of a line item and the amount to allocate.

The other loop is the main loop that allocates according to a calculation.

This fixes it so that the allocation is correctly merged in if passed in in
getPayableLineItems and from that point we only need one loop.

This simplification is tested via the testCreatePaymentLineItems
which I cleaned up and made more robust. I was able to step through it in #15685 and identify how
it was working

Comments

@kcristiano @monishdeb @pradpnayak can one of you look at this ? We merged one PR in this area relating to allocations but in our digging found other breakage - notably in the refund handling.

I want to get a few preliminary PRs merged - this one
#15640 & #15687 but I want all these fixes to hit 5.20

[civibot]

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[eileenmcnaughton]

test this please

[eileenmcnaughton]

test this please

[colemanw]

Code certainly looks better. How's the test coverage?

[eileenmcnaughton]

Test coverage is good on this

[kcristiano]

@eileenmcnaughton It appears that this is also in #15705

[seamuslee001]

@kcristiano i think @eileenmcnaughton is treating that as the "complete package" so to speak but this is a part that can be packaged up separately and merged if you think its ok