Fixes CVE-2021-21341, CVE-2021-21342, CVE-2021-21343, CVE-2021-21344,
CVE-2021-21345, CVE-2021-21346, CVE-2021-21347, CVE-2021-21348,
CVE-2021-21349, CVE-2021-21350 and CVE-2021-21351.
* gnu/packages/xml.scm (java-xstream): Update to 1.4.16.
[inputs]: Add java-mxparser, a fork of java-xpp3 made by upstream.
Java-xpp3 is still needed.
Signed-off-by: Julien Lepiller <julien@lepiller.eu>