[Feature request] Structure handling functions.

Some way to load and maybe save NBT structures to the same place that structure blocks save and load them from.
Or load the NBT files from any file location that its allowed to access.

Maybe a function like `structure_load(structureName, locationArray, [rotation], [mirror])` to load a saved structure into the world.

So if I use a command block to save a structure named "minecraft:test", i could load it with CommandHelper using
`structure_load("minecraft:test", ploc("Steve"))`
to place it at Steve's location for example

No source files, tests, or entry points are named. Start by tracing how CommandHelper registers functions and how Minecraft structure blocks save and load NBT structures; done should be a settled API that can place a named structure at a location, with the requested optional rotation and mirror behavior, while clarifying whether arbitrary accessible NBT files are supported.

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