Introduce Catch's own RNG based on the PCG family of RNGs

In the future, we will also want to introduce our own
`uniform_int_distribution` and `uniform_real_distribution` to get
repeatable test runs across different platforms.

include/internal/catch_test_case_registry_impl.cpp

@@ -11,6 +11,7 @@
 #include "catch_enforce.h"
 #include "catch_interfaces_registry_hub.h"
 #include "catch_random_number_generator.h"
+#include "catch_run_context.h"
 #include "catch_string_manip.h"
 #include "catch_test_case_info.h"