No information on what exactly is the offset/direction argument in //move and //stack

The only way to find out what exactly is the second argument of `//move` and `//stack` commands, is to use it wrong and read the error message, and even then it's not exactly accurate:

```
//stack 3 12
Usage: //stack [-abers] [count] [offset] [-m ]
Invalid value for [offset] (Unknown direction: 12), acceptable
values are 'me' to use facing direction, or any direction, or
any block vector with x, y, z
```

First, the small thing: it would be better to write "any block vector with x,y,z", without spaces between xyz, because you can't write this in the command with spaces (unless you put this in quotation marks). Second, I don't think it's exactly "block" vector. I thought that when I have 3x3x3 region and I'm doing `//stack 1 1,0,0`, the region will be copied to the east, one block apart. Actually, it's copied one region length apart, 3 blocks in this case. So e.g. `//stack 1 2,0,0` will give me 6 blocks between the two copies of the region. So it would be better to drop "block" from "block vector" in the `//stack` command, because it's not the blocks we're translating. In the `//move` command that vector is really a block vector, so it's good.

What is in the documentation is also a little inconsistent, as the [manual](https://worldedit.enginehub.org/en/latest/usage/regions/regionops/#stacking) names that argument "direction", but the [command reference](https://worldedit.enginehub.org/en/latest/commands/#region-commands) names it "offset". Now that's understandable as the manual doesn't mention that this argument is really an offset rather than a direction (that "east" is converted to "1,0,0"), but I think it can be confusing when you're using `//move` and learned that the second arg is a direction, but then you use help command, and it tells you that it's an offset. Like how can the direction be an offset, when we're passing the number of blocks in the first arg?

If I knew earlier how these commands work, I would be much more efficient with them, so I think it's worthwhile to explain them exhaustively.