Add the merge_dictionaries utility function.

utilities/merge-dictionaries.typ

@@ -0,0 +1,35 @@
+/// Merge dictionaries together by recursively going through each key. Any
+/// non-dictionary keys will be overwritten by whichever value comes last.
+#let merge_dictionaries(
+  /// When two array are found for the same key, merge them together.
+  merge_arrays: true,
+  ..args,
+) = {
+  let output = (:)
+
+  for arg in args.pos() {
+    assert.eq(type(arg), dictionary, message: "Can't merge non-dictionary types.")
+
+    for (key, value) in arg {
+      if key not in output {
+        output.insert(key, value)
+        continue
+      }
+
+      let value_type = type(value)
+      let existing_type = type(output.at(key))
+
+      if value_type == dictionary and existing_type == dictionary {
+        output.at(key) = merge_dictionaries(output.at(key), value)
+      } else if merge_arrays and value_type == array and existing_type == array {
+        for item in value {
+          output.at(key).push(item)
+        }
+      } else {
+        output.at(key) = value
+      }
+    }
+  }
+
+  return output
+}