Pages TCK compliance with pages 4.0 and EL 6.0 apis

[alwin-joseph]

Describe the change

Changes to build the Pages TCK with latest APIs Pages 4.0 and EL 6.0.

• Delete the testing of removed methods from JSP 4.0 (elexception, elparseexception, expression, expressionevaluator , variableresolver)
• Avoid usage of removed getFeatureDescriptors() method in EL 6.0
• Replace jakarta.servlet.jsp.el.ELException with jakarta.el.ELException
• Delete the removed classes jakarta.servlet.jsp.el.ExpressionEvaluator & jakarta.servlet.jsp.el.VariableResolver from JSP4.0
• Delete usage of FunctionMapper
• Delete tests pageContextGetExpressionEvaluatorTest, pageContextGetVariableResolverTest and jspExceptionGetRootCauseTest
• Replace getRootCause() with getCause() for JspException class

Pending/TODO for staging Pages TCK:

• To update the documentation wrt the latest api and refactored TCK.
• Add standalone signature test

Additional context
Referred the PR jakartaee/pages#234 that removed the deprecated api methods.

cc @markt-asf @gurunrao @arjantijms