feat(content): Repave the road to Isherwood Farm

[Zlorthishen]

Purpose of change

to fix the Isherwood Farm not having a valid road connection, as well as making sure that the internal fields and forests aren't overwritten

Describe the solution

adds the map terrain special_forest, special_forest_thick, and special_field, replaces all old instances in 'Isherwood farm`
adds a road connection to the overmap_special

Describe alternatives you've considered

Testing

spawned several dozen instances of isherwood farms on a locally compiled copy. altered a few things to ensure no strange map_extras get spawned within the farm

Additional context

Checklist

[autofix-ci]

Autofix has formatted code style violation in this PR.

I edit commits locally (e.g: git, github desktop) and want to keep autofix

1. Run git pull. this will merge the automated commit into your local copy of the PR branch.
2. Continue working.

I do not want the automated commit

1. Format your code locally, then commit it.
2. Run git push --force to force push your branch. This will overwrite the automated commit on remote with your local one.
3. Continue working.

If you don't do this, your following commits will be based on the old commit, and cause MERGE CONFLICT.

[scarf005]