allow json (#1137)

Allow creating .json files.
Also added the json language server so syntax highlighting and validation works with the ingame editor

src/Paths/TextFilePath.ts

@@ -7,7 +7,7 @@ export type TextFilePath = FilePath & WithTextExtension;
 
 /** Check extension only */
 export function hasTextExtension(path: string): path is WithTextExtension {
-  return path.endsWith(".txt");
+  return path.endsWith(".txt") || path.endsWith(".json");
 }
 
 /** Sanitize a player input, resolve any relative paths, and for imports add the correct extension if missing */