Add a variety of marine plants

[Procyonae]

Summary

Content "Adds a variety of marine plants."

Purpose of change

Revives #71844, splitting the bugfixes to a different PR

Describe the solution

Most of this is just fairyarmadillos original PR so see that
Makes the kelp patches they gave up on spawn (I think they were just missing the "extras" entry on the overmap_terrain)
Adds a kelp forest mutable which heavily cargo cults the meadow mutable bc fairyarmadillo appeared to be trying to do a multitile map extra which isn't a thing you can do (in json at least)

Describe alternatives you've considered

I don't think we have any way to place a mutables root at non z0 zlevels which is kinda ugly but I don't feel like adding code to deal with that rn and it's easy enough to work around
I've no idea how large, varied in size or what shape kelp forests tend to be irl and don't really feel like researching it, tweaking both is pretty simple tho

Testing

Kelp patch

Example kelp forest

Example kelp forest layouts

Additional context

[github-actions]

Spell checker encountered unrecognized words in the in-game text added in this pull request. See below for details.

Click to expand

• Also known as kombu, this brown algae grows in a single leaflike blade that can reach more than twice the height of a man. Young fronds make for excellent soup stock and can even be eaten raw.
• Sometimes known as green laver, this leafy algae from the Ulva genus grows in leafy little patches around shallows and tide pools. Though small, it makes a tasty snack.

This alert is automatically generated. You can simply disregard if this is inaccurate, or (optionally) you can also add the new words to tools/spell_checker/dictionary.txt so they will not trigger an alert next time.

Hints for adding a new word to the dictionary

• If the word is normally in all lowercase, such as the noun word or the verb does, add it in its lower-case form; if the word is a proper noun, such as the surname George, add it in its initial-caps form; if the word is an acronym or has special letter case, such as the acronym CDDA or the unit mW, add it by preserving the case of all the letters. A word in the dictionary will also match its initial-caps form (if the word is in all lowercase) and all-uppercase form, so a word should be added to the dictionary in its normal letter case even if used in a different letter case in a sentence.
• For a word to be added to the dictionary, it should either be a real, properly-spelled modern American English word, a foreign loan word (including romanized foreign names), or a foreign or made-up word that is used consistently and commonly enough in the game. Intentional misspelling (including eye dialect) of a word should not be added unless it has become a common terminology in the game, because while someone may have a legitimate use for it, another person may spell it that way accidentally.

[worm-girl]

fairyarmadillo appeared to be trying to do a multitile map extra which isn't a thing you can do (in json at least)

Gonna be real with you, I had no idea what I was doing with map stuff lol.

[Procyonae]

Gonna be real with you, I had no idea what I was doing with map stuff lol.

If you want any help with future stuff just gimme a shout anywhere ^^