[Docs] Added {.experimental: "codeReordering".} to manual

[awr1]

Closes #8699.
Might also for #8822. (depends on if {.reorder.} needs new impl)

[awr1]

Something to add wrt declared:

{.reorder: on.}

proc x() =
  echo(declared(foo))

var foo = 4

x() # "false", the same as it would be with {.reorder: off.}

Should this be defined behavior (in which case I will clarify in the docs) or is this an issue?

[Araq]

Should this be defined behavior (in which case I will clarify in the docs) or is this an issue?

The last time I thought about it, it seems to break less code the way it's handled now.

[Araq]

Ok, but shouldn't this become {.experimental: "reorder".} before we document it?

[dom96]

Why not just remove this? It's just a distraction to keep it there I think.

[zah]

This is hidden at the moment, right? I'm still in favor of noforward as a more comprehensive solution and I hope to work on it in the future.

[awr1]

It's commented out in case it becomes relevant again. (if you really really want me to I'll remove it)

[awr1]

Changed the stuff to {.experimental: "codeReordering".} and moved everything to the scope section (if you think there's a better place to put it, let me know. Also commented out the declared() section since the way it works right now is not entirely obvious. It'd be better to just have the get this all in the docs as an experimental feature at least then decide how to deal with that later.

If we're going with #8875, please merge that before/same time as this.