[TestBug] Ignore two failing FXML unit tests which use Nashorn script engine

Two of the FXML unit tests use the Nashorn JavaScript engine to test the FXML scripting capability. Nashorn has been deprecated since JDK 11 and has been removed in JDK 15.

When running with JDK 15-ea these two tests fail (as expected, since Nashorn is gone).

test.javafx.fxml.FXMLLoader_ScriptTest > testScriptHandler FAILED
    javafx.fxml.LoadException: Page language not specified.
    /C:/Users/kcr/javafx/jfx-kcr/jfx/rt/modules/javafx.fxml/build/resources/test/test/javafx/fxml/script_handler.fxml:35
        at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2625)
        at javafx.fxml/javafx.fxml.FXMLLoader$ScriptElement.processCharacters(FXMLLoader.java:1604)
        at javafx.fxml/javafx.fxml.FXMLLoader.processCharacters(FXMLLoader.java:2855)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2566)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2470)
        at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2439)
        at test.javafx.fxml.FXMLLoader_ScriptTest.testScriptHandler(FXMLLoader_ScriptTest.java:134)

test.javafx.fxml.FXMLLoader_ScriptTest > testExternalScriptHandler FAILED
    javafx.fxml.LoadException: Unable to locate scripting engine for extension js.
    /C:/Users/kcr/javafx/jfx-kcr/jfx/rt/modules/javafx.fxml/build/resources/test/test/javafx/fxml/script_handler_external.fxml:31
        at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2625)
        at javafx.fxml/javafx.fxml.FXMLLoader$ScriptElement.processStartElement(FXMLLoader.java:1544)
        at javafx.fxml/javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2726)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2556)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2470)
        at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2439)
        at test.javafx.fxml.FXMLLoader_ScriptTest.testExternalScriptHandler(FXMLLoader_ScriptTest.java:147)


These tests should be ignored if Nashorn script engine is not available.

In future, these tests will be rewritten/replaced under JDK-8245568.