feat: Shopping List Editor Improvements

[michael-genson]

What type of PR is this?

(REQUIRED)

• feature

What this PR does / why we need it:

(REQUIRED)

This adds a few QoL improvements to the shopping list, some of which are discussed in #3118 (warning: opinions contained within):

• When creating a new item, the quantity defaults to zero instead of one. Generally, when shopping, you're not specifying the specific quantity (e.g. "Buy Salt" or "Buy Garlic"), and a "zero" quantity effectively just hides the quantity. If you want specific quantities, it's almost always related to a recipe, and adding a recipe to a shopping list already handles the quantity for you anyway. Or, if you actually want to input the quantity on an ad hoc item, it's no more likely to be a quantity of "1" than any other value
• When selecting a food, the label of the item is automatically updated (if you want the label to be different, you can change it after choosing the food).
• After you create an item, if you toggled "is food", the next item you create will also have "is food" toggled

See below for a demo of these features; Note in the demo: "salt" and "apple" have foods assigned, but no other foods do.

Which issue(s) this PR fixes:

(REQUIRED)

Fixes #2910

Testing

(fill-in or delete this section)

Manually, see above

[boc-the-git]

LGTM