feat: [closes #408] Salt

What this PR does

For #408 (and in service of #380), this PR adds Salt Rock mining and a Salt recipe. Additionally, it:

Adds Salt as an ingredient to some preexisting recipes
Refactors resource factory code to have a shared (pseudo) interface
Tweaks Stone spawning logic to make Stones spawn slightly less frequently
- This is done to balance against the additional spawning of Salt Rocks

How this change can be validated

To quickly give yourself the Shovel and a lot of money, first set yourself just below level 6:

window.farmhand.setState({
  itemsSold: { carrot: 2499 },
  inventory: [{ id: "carrot", quantity: 50 }],
  money: 1000000,
})

And then sell a Carrot to unlock the Shovel.

From there, go to the Field and mine until you get a Salt Rock. To unlock the Salt recipe, sell 30 Salt Rocks. Salt should also be shown as an ingredient for:

French Onion Soup
Hot Sauce
Garlic Fries
Sweet Potato Fries
Onion Rings

Questions or concerns about this change

I chose not to make Salt an unlock condition of the recipes that now use it as an ingredient. If that wasn't the case, some players would see their recipes mysteriously disappear until they sell some Salt. Additionally, letting the Salt-using recipes be unlocked earlier indicates that Salt exists, which is a mid-game item. So, hopefully this all balances out by giving players more goals to work towards.

It's worth mentioning that the addition of Salt as an ingredient will make recipes that now use it more valuable.

Additional information

Salt Rock

Salt Recipe

jeremyckahn / farmhand