feat: list reporters

[RixInGithub]

these things

(notice how the reporter is a bit darker, like the lists orange rather than the variables orange)

listReporters.sb3.zip

ik this is useless but maybe this will be useful for someone else idk im too lazy to write

could be useful for joining lists by some delimeter which is hardcoded in scratch-vm internally

[aspizu]

This already works? Just write the name of the list and it becomes a list reporter if the list exists. We already use this as an optimization for some std/string functions (see strbuf list)

[RixInGithub]

This already works?

idk tbh

# This is a sprite.
costumes "blank.svg";
list something;

proc what l {
  say l, 2;
}

# when green flag clicked
onflag {
  add "idk" to something;
  what something;
}

yeah pretty silly edge case if you ask me, idk