Simplify prescription line edit

[lache-melvin]

👩🏻‍💻 What does this PR do?

Sadly did not get time to finish this, but have implemented separate to existing prescription line edit so can compare. A few pieces still missing but hopefully the thinking is helpful

Some experiments:

• Splitting into more components - each should have one job
  • Hopefully easier to follow based on what you see in UI, though I think this could improve further
• Helpers into own, testable files where possible
• Save on each item, one less layer of data management
• State management only where needed, rather than "see item has changed, clear this"
• Stripping out some logic for
• Returning items from backend on invoice node - helpful for line edit list, but also think we should use this for things like item directions, prescribed quantity...

💌 Any notes for the reviewer?

🧪 Testing

• (e.g.) Central Sync server with 1 Legacy Desktop remote site and 1 OMS remote site running this PR
• (e.g.) This sample datafile: google drive link
• (e.g.) Open a requisition with some lines
• (e.g.) Make a couple invoices supplying some amount of those lines
• (e.g.) Review that "issued" column is the sum of the amount already issued in invoices for this requisition

📃 Documentation

• Part of an epic: documentation will be completed for the feature as a whole
• No documentation required: no user facing changes or a bug fix which isn't a change in behaviour
• These areas should be updated or checked:
  1.
  2.

📃 Reviewer Checklist

The PR Reviewer(s) should fill out this section before approving the PR

Breaking Changes

• No Breaking Changes in the Graphql API
• Technically some Breaking Changes but not expected to impact any integrations

Issue Review

• All requirements in original issue have been covered
• A follow up issue(s) have been created to cover additional requirements

Tests Pass

• Postgres
• SQLite
• Frontend

[lache-melvin]

Closing as too far behind develop, best to apply from scratch when we make time for this work