Option to start a world with a pre-filled Inventory

Since you're now able to start a world with changed Gamerules, why not a pre-filled Inventory as well? Options are restricted to what's in the Creative inventory, and anything that can be enchanted can come pre-enchanted. Applications include, but aren't limited to:

- starting an adventure with one Shulker Box as a starting backpack

- playing through a Hardcore world with a set of Leather Armor with Unbreaking III, Mending, and Curse of Binding as a handicap

- spawning in the "Classic Flat" Superflat preset with 12 End Portal Frames

- playing on a "deserted island" seed, bringing with you two spawn eggs of every animal to raise

- starting a Nether-only playthrough by giving yourself 10 blocks of Obsidian and a Fire Charge

- giving yourself full enchanted Netherite gear just for the lols