Move c-like comment to javadoc in TextMapPropagator (#2930)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

api/context/src/main/java/io/opentelemetry/context/propagation/TextMapPropagator.java

@@ -88,11 +88,15 @@ public interface TextMapPropagator {
    * clear fields as they couldn't have been set before. If it is a mutable, retryable object,
    * successive calls should clear these fields first.
    *
+   * <p>Some use cases for this are:
+   *
+   * <ul>
+   *   <li>Allow pre-allocation of fields, especially in systems like gRPC Metadata
+   *   <li>Allow a single-pass over an iterator
+   * </ul>
+   *
    * @return the fields that will be used by this formatter.
    */
-  // The use cases of this are:
-  // * allow pre-allocation of fields, especially in systems like gRPC Metadata
-  // * allow a single-pass over an iterator
   Collection<String> fields();
 
   /**