Added editorutils file with a utility function to convert mimetype to editor modes

functions/editorutils.js

@@ -0,0 +1,11 @@
+const mimeToMode = {
+  "text/plain": "plain_text",
+  "text/html": "html",
+  "application/xml": "xml",
+  "application/hal+json": "json",
+  "application/json": "json"
+}
+
+export function getEditorLangForMimeType(mimeType) {
+  return mimeToMode[mimeType] || "plain_text";
+}