Add a way to manipulate nbt of blocks in selection

### The Problem

It is extremely tiresome to use worldedit to set LootTables for chests in an area, without destroying their other NBT data.
Or to fix up decorated pot patterns without touching their content.
Or to basically do any non-destructive nbt operation

### A Solution

Add a command/commands to basically mass execute /data merge block {nbt], /data set block {nbt} and /data modify block ...

e.g.:
`//nbtmerge chest {LootTable:"chests/simple_dungeon"}`
`//nbtset {}`
`//nbtmodify decorated_pot shards[0] set "minecraft:skull_pottery_sherd"`

Maybe warn players that bad NBT may crash the game, especially with modded blocks when first using the command.

### Alternatives

Alternatively just allow arbitrary commands to be executed for blocks in selection matching mask.

//execute [mask] command [arguments] §x §y §z [arguments]

Pro:
- more versatile

Con:
- less readable/intuitive commands

### Anything Else?

_No response_