Return a copy of responseHeaders in getResponseHeaders

Return a new HashMap instance of responseHeaders to prevent external modifications.

Author: bolivir

android/capacitor/src/main/java/com/getcapacitor/WebViewLocalServer.java

@@ -129,7 +129,7 @@ public String getReasonPhrase() {
         }
 
         public Map<String, String> getResponseHeaders() {
-            return responseHeaders;
+            return new HashMap<>(responseHeaders);
         }
     }