Add a new reporter customization point: reporting all assertions

By opting the JUnit and XML reporters into it, we no longer run
into problem where they underreport the results without `-s` flag.

Related to #1264, #1267, #1310

include/reporters/catch_reporter_xml.cpp

@@ -24,6 +24,7 @@ namespace Catch {
         m_xml(_config.stream())
     {
         m_reporterPrefs.shouldRedirectStdOut = true;
+        m_reporterPrefs.shouldReportAllAssertions = true;
     }
 
     XmlReporter::~XmlReporter() = default;