WebView: Allow to load style sheet from jlink images

Currently, loading a style sheet file using `WebView.getEngine().setUserStyleSheetLocation(url)` fails if the url start's with `jrt`, i.e. if the file is packaged in an application image using jlink. This is fixed with this PR.

Author: tobiasdiez

modules/javafx.web/src/main/java/javafx/scene/web/WebEngine.java

@@ -491,7 +491,7 @@ public final BooleanProperty javaScriptEnabledProperty() {
      * Location of the user stylesheet as a string URL.
      *
      * <p>This should be a local URL, i.e. either {@code 'data:'},
-     * {@code 'file:'}, or {@code 'jar:'}. Remote URLs are not allowed
+     * {@code 'file:'}, {@code 'jar:'}, or {@code 'jrt:'}. Remote URLs are not allowed
      * for security reasons.
      *
      * @defaultValue null
@@ -554,6 +554,7 @@ public final StringProperty userStyleSheetLocationProperty() {
                         dataUrl = url;
                     } else if (url.startsWith("file:") ||
                                url.startsWith("jar:")  ||
+                               url.startsWith("jrt:")  ||
                                url.startsWith("data:"))
                     {
                         try {