Replace CppUnit with Catch for unit tests

Drop the legacy CppUnit testing framework used for the unit tests.
Replacing it with Catch has the advantage of not requiring CppUnit
libraries to be installed on the system in order to be able to run
tests (Catch is header-only and a copy of it is now included in the
main repository itself) and, in the future, of being able to write
the tests in a much more natural way.

For now, however, avoid changing the existing tests code as much as
[reasonably] possible to avoid introducing bugs in them and provide
the CppUnit compatibility macros in the new wx/catch_cppunit.h header
which allow to preserve the 99% of the existing code unchanged. Some
of the required changes are:

 - Decompose asserts using "a && b" conditions into multiple asserts
   checking "a" and "b" independently. This would have been better
   even with CppUnit (to know which part of condition exactly failed)
   and is required with Catch.

 - Use extra parentheses around such conditions when they can't be
   easily decomposed in the arrays test, due to the use of macros.
   This is not ideal from the point of view of messages given when
   the tests fail but will do for now.

 - Rewrite asserts using "a || b" as a combination of condition
   checks and assert macros. Again, this is better anyhow, and is
   required with Catch. Incidentally, this allowed to fix a bug in
   the "exec" unit test which didn't leave enough time for the new
   process to be launched before trying to kill it.

 - Remove multiple CPPUNIT_TEST_SUITE_NAMED_REGISTRATION() macros,
   our emulation of this macro can be used only once.

 - Provide string conversions using Catch-specific StringMaker for
   a couple of types.

 - Replace custom wxImage comparison with a Catch-specific matcher
   class.

 - Remove most of test running logic from test.cpp, in particular don't
   parse command line ourselves any longer but use Catch built-in
   command line parser. This is a source of a minor regression:
   previously, both "Foo" and "FooTestCase" could be used as the name of
   the test to run, but now only the latter is accepted.

tests/testprec.h

@@ -4,7 +4,7 @@
 #include "wx/wxprec.h"
 #include "wx/stopwatch.h"
 #include "wx/evtloop.h"
-#include "wx/cppunit.h"
+#include "wx/catch_cppunit.h"
 
 // Custom test macro that is only defined when wxUIActionSimulator is available
 // this allows the tests that do not rely on it to run on platforms that don't
@@ -173,21 +173,9 @@ void DeleteTestWindow(wxWindow* win);
 
 #endif // wxUSE_GUI
 
-// Macro that can be used to register the test with the given name in both the
-// global unnamed registry so that it is ran by default and a registry with the
-// same name as this test to allow running just this test individually.
-//
-// Notice that the name shouldn't include the "TestCase" suffix, it's added
-// automatically by this macro.
-//
-// Implementation note: CPPUNIT_TEST_SUITE_[NAMED_]REGISTRATION macros can't be
-// used here because they both declare the variable with the same name (as the
-// "unique" name they generate is based on the line number which is the same
-// for both calls inside the macro), so we need to do it manually.
-#define wxREGISTER_UNIT_TEST(name) \
-    static CPPUNIT_NS::AutoRegisterSuite< name##TestCase > \
-        CPPUNIT_MAKE_UNIQUE_NAME( autoRegisterRegistry__ ); \
-    static CPPUNIT_NS::AutoRegisterSuite< name##TestCase > \
-        CPPUNIT_MAKE_UNIQUE_NAME( autoRegisterNamedRegistry__ )(#name "TestCase")
+// Convenience macro which registers a test case using just its "base" name,
+// i.e. without the common "TestCase" suffix, as its tag.
+#define wxREGISTER_UNIT_TEST(testclass) \
+    wxREGISTER_UNIT_TEST_WITH_TAGS(testclass ## TestCase, "[" #testclass "]")
 
 #endif