(cherry picked from commit e812b6ce)

MockFilterChain should not be re-used across requests. This is not an
issue unless tests are executed concurrently. This change ensures the
MockFilterChain is re-created for each request in MockMvc.

Issue: SPR-10838

ResourceHttpMessageConverter tries to use the filename to determine the
media type, but for Resource implementations such as ByteArrayResource
it is null, which causes NullPointerException. The fix checks whether
getFilename returns null before attempting to determine the media type
by it.

Issue: SPR-10848

Issue: SPR-10819
(cherry picked from commit ea6525f1)

Added support for StreamSources that do not have a InputStream or
Reader, but do have a System ID.

Issue: 10828

(cherry picked from 5549bd90)

Added reference to CatchAllConverter in both javadoc and reference docs.

Issue: SPR-10821

Added XStream CatchAllConverter that supports all classes, but throws
exceptions for (un)marshalling.

Main purpose of this class is to register this converter as a catchall
last converter with a normal or higher priority in addition to
converters that explicitly  support the domain classes that should be
supported. As a result, default XStream  converters with lower
priorities and possible security vulnerabilities do not get invoked.

Issue: SPR-10821

Issue: SPR-10817

Disable by default external entity resolution when using Spring OXM
with jaxb. This prevents a XML entity from being able to resolve a
local file on the host system.

See:
https://www.owasp.org/index.php/XML_External_Entity_(XXE)_Processing

Issue: SPR-10806
(cherry picked from commit 75762748)

Change "fluid" interface to "fluent" and "string" to "chain", plus fix
few typos in Javadoc.

Issue: SPR-10792
(cherry picked from commit 2344412e)

Issue: SPR-10581
(cherry picked from commit 2626a35f)

Issue: SPR-10421

Also setting the bean class loader on the XStream instance itself now.

Issue: SPR-10421

Issue: SPR-10413
(cherry picked from commit c26272ce)

Issue: SPR-10604
(cherry picked from commit f329140d)

Issue: SPR-10713

Issue: SPR-10648

Issue: SPR-10777

Issue: SPR-10788

Issue: SPR-10752
Issue: SPR-10627

Issue: SPR-10767

Issue: SPR-10752
Issue: SPR-10627

PropertySourcesPlaceholderConfigurer's "ignoreUnresolvablePlaceholders" setting reliably applies to nested placeholders as well

Issue: SPR-10549
(cherry picked from commit 127b91fd)

Issue: SPR-10775

Issue: SPR-10775

Issue: SPR-10775

Issue: SPR-10609

Issue: SPR-10509