Bug for Quantity Change Modal

[kyl-dc]

When selecting an item that was added before the latest one, the quantity change modal that opens up ends up being blocked by some elements on the screen. This might be because the FlatList item z-index follows the ordering of items as they're added, so clicking a previously added item shows this:

Steps to replicate:

• checkout 39_quantityChangeModal
• Add item 3 and item 4 with some tags
• Select the quantity field on item 2

Solution Approach:
Find a way to make the selected item's z-index greater than the other list items, so it stays on top of the screen. OR, Find a way to re-implement how we show our listItems without using FlatList.
I found this issue as well: facebook/react-native#28751
Here, there's a proposed solution by bboure on Aug 22, 2020 maybe try something like that.

Additional Changes:

• Fix the the quantity styling so that it's identical for both the AddItemModal and the QuantityChangeModal, with subtract on the left. ie. (-) 1 (+)

• Make sure that the subtract (-) button is greyed-out when it hits 1, as quantities need to be >0.