Update FaceletViewDeclarationLanguageStrategy to look at exact mappings to the Faces Servlet

While investigating the 4.1 TCK tests, a 404 was returned for some pages in the headAndBodyRenderer app. Only the `*.xhtml` extensions worked even though the servlet mappings were listed:

web.xml:

    <servlet>
        <servlet-name>facesServlet</servlet-name>
        <servlet-class&amp;gt;jakarta.faces.webapp.FacesServlet</servlet-class&amp;gt;
    </servlet>
    <servlet-mapping>
        <servlet-name>facesServlet</servlet-name>
        <url-pattern>*.xhtml</url-pattern>
        <url-pattern>*.xhtmlAsXhtml</url-pattern>
        <url-pattern>*.xhtmlAsXml</url-pattern>
    </servlet-mapping>

Turns out that our FaceletViewDeclarationLanguageStrategy class looked if *.xhtml matched, and if not, then it looked at any mappings set via jakarta.faces.FACELETS_VIEW_MAPPINGS.  This isn't set in the app. Ultimately, FaceletViewDeclarationLanguageStrategy#handlesView returns false and since no VDL is found, the page fails to load.

https://github.com/apache/myfaces/blob/7f6fefb4b05ccf5272e6907397954f7d4db8f4d2/impl/src/main/java/org/apache/myfaces/view/facelets/FaceletViewDeclarationLanguageStrategy.java#L62-L76 

I think we should update the code to look at the servlet mappings, too.