Prior to this commit, when adding a ShallowEtagHeaderFilter to an
application, the ServletResponse would be wrapped by a
ContentCachingResponseWrapper. When any part of the Spring
infrastructure calls `flushBuffer` on the wrapped response, the call is
delegated to the actual response, which is committed. It's not possible
to alter the response (headers, content) anymore - the ETag filter can't
act.

This change prevents the `flushBuffer` call to be delegated and only
commits the underlying response once the cached content is copied to the
actual response stream.

Issue: SPR-13717

With this change the MapAccessor now extends CompilablePropertyAccessor
rather than just PropertyAccessor. This means that any expression that
ends up using the MapAccessor is now compilable for fast performance.

Issue: SPR-13638

* pr/926:
  Add link in jsp tag library

Closes gh-926

Issue: SPR-13678

* pr/923:
  Remove invalid underscore

Closes gh-923

* pr/922:
  Add quotes around attribute value

Closes gh-922

This upgrade includes AutoCloseable support for HtmlUnit WebConnections as introduced in 2.19, while remaining compatible with 2.18.

Issue: SPR-13686

Issue: SPR-13680

Issue: SPR-13680

Issue: SPR-13680

Issue: SPR-13621

Issue: SPR-13655

Issue: SPR-13650

Issue: SPR-13674

Issue: SPR-13669

Issue: SPR-13671

Issue: SPR-13587, SPR-13643

Issue: SPR-13637

Issue: SPR-13668

Issue: SPR-13665

Issue: SPR-13667

Issue: SPR-13666

Issue: SPR-13663