[REQUEST] System to make item shops easier

[liana-p]

Is your feature request related to a problem? Please describe.
Buying items is a common need in games with items.

Doing so involves creating choice menus with conditions and checking currency/removing cost etc, which is a lot of manual work. Would be nice to have an engine feature for this.

Describe the solution you'd like
Shops could be defined in yaml files that would list available items, price, and which currency they use (from hud stats that can be used as currency).
Then creating a shop could be an option in choice instructions to use the shop and populate the choice menu with the items in the shop

More complex use cases might want to manually add/delete items from shops though, so maybe the shop should take an array of items, and it's up to the game to either load that from a yaml file, or generate it dynamically.

Then shops could show options to purchase item with name/icon of the item, cost, greyed choice if not enough money etc, and automatically handle taking the money and adding the item

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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