Changes

xml: Implement configuration extension for xml analysis

This patch uses the recently added extension point for configuration
source `org.eclipse.tracecompass.tmf.core.config.xmlsourcetype` for
XML analysis. The purpose of the extension point is to standardize
how configurations are managed in Trace Compass.

This commit includes JUnit tests for the XmlConfigurationSource class.

[Added] Implementation of a configuration extension for xml analysis

Change-Id: I9b035f25eaef9dd98250801040f4fa6bf1d60f4b
Signed-off-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/c/tracecompass/org.eclipse.tracecompass/+/204456
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Trace Compass Bot <tracecompass-bot@eclipse.org>
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>