Nonstandard ItemPrototypeFilter field for prototypes.get_item_filtered

[protocol_1903]

Normally, when using the API, fields/keys always follow the pattern of lowercase letters with underscores as separators between words. However, for the fuel-category search filter when filtering for item prototypes, the key is "fuel-category" instead of the expected "fuel_category". This is unintuitive and doesn't feel right, as now you need to use {["fuel-category"] = "chemical"} instead of just {fuel_category = "chemical"}. Though this is a breaking change, it's minor enough that I feel it should be done now while 2.1 is still unstable.