Use response encoding when escaping HTML

With SPR-9293, it is now possible to HTML escape text while taking into
account the current response encoding. When using UTF-* encodings, only
XML markup significant characters are escaped, since UTF-* natively
support those characters.

This commit adds a new servlet context parameter to enable this fix by
default in a Spring MVC application:

    <context-param>
      <param-name>responseEncodedHtmlEscape</param-name>
      <param-value>true</param-value>
    </context-param>

Issue: SPR-12350, SPR-12132