Clarify whether javax.servlet.error.exception_type and javax.servlet.error.exception refer to a wrapped or unwrapped ServletException

From section 10.9.2 Error Pages:

> If no error-page declaration containing an exception-type fits using the class-
> hierarchy match, and the exception thrown is a ServletException or subclass
> thereof, the container extracts the wrapped exception, as defined by the
> ServletException.getRootCause method. A second pass is made over the error
> page declarations, again attempting the match against the error page declarations,
> but using the wrapped exception instead.

This section does not make clear when a ServletException is thrown that contains a wrapped exception, if the values of the request attributes `javax.servlet.error.exception_type` and `javax.servlet.error.exception `should be the unwrapped exception or not.

Setting them to the unwrapped exception will remove stacktrace information that may be valuable.

On the other hand, the current servlet-tck seems to test that the values are unwrapped - see https://github.com/eclipse-ee4j/jakartaee-tck/blob/master/src/com/sun/ts/tests/servlet/spec/errorpage/URLClient.java#L76

Read section 10.9.2, “Error Pages,” and compare its wording with the servlet-TCK check in src/com/sun/ts/tests/servlet/spec/errorpage/URLClient.java at line 76. Determine whether javax.servlet.error.exception_type and javax.servlet.error.exception should expose the wrapped or unwrapped exception, then clarify the specification and align the test expectation.

Written by the indexing model from the issue text.