Fix uploader for metadata containing '%' (#1192)

I noticed that this was broken again actually. It seems like there was
already code in place to deal with that, but OC probably changed? In any
case, this solution is cleaner and seems to work fine.

frontend/src/routes/Upload.tsx

@@ -1027,7 +1027,7 @@ const finishUpload = async (
         // Add metadata in DC-Catalog
         {
             const dcc = constructDcc(metadata, user);
-            const body = new FormData();
+            const body = new URLSearchParams();
             body.append("mediaPackage", mediaPackage);
             body.append("dublinCore", dcc);
             body.append("flavor", "dublincore/episode");
@@ -1067,16 +1067,9 @@ const finishUpload = async (
 
 /**
  * Encodes a value for inclusion in XML sent to Opencast.
- *
- * For one, we need to escape some characters for XML inclusion. But Opencast
- * also tries to URI-decode the value, meaning that `%` in the original value
- * will be interpreted as encoded characters, which usually fails. So if the
- * original value contains `%`, we URI-encode it.
  */
-const encodeValue = (value: string): string => {
-    const escapedXml = new XMLSerializer().serializeToString(new Text(value));
-    return escapedXml.includes("%") ? encodeURIComponent(escapedXml) : escapedXml;
-};
+const encodeValue = (value: string): string =>
+    new XMLSerializer().serializeToString(new Text(value));
 
 /** Creates a Dublin Core Catalog in XML format that describes the given metadata. */
 const constructDcc = (metadata: Metadata, user: User): string => {