Add deprecation warning in ParseAndCatchTests

Parsing C++ with regex in CMake is error prone and regularly leads to silently
dropped (not run) test cases.

Going forward the function `catch_discover_tests` from `contrib/CMake.cmake`
should be used.

For more information see https://github.com/catchorg/Catch2/issues/2092#issuecomment-747342765

extras/ParseAndAddCatchTests.cmake

@@ -241,6 +241,7 @@ endfunction()
 
 # entry point
 function(ParseAndAddCatchTests TestTarget)
+    message(DEPRECATION "ParseAndAddCatchTest: function deprecated because of possibility of missed test cases. Consider using 'catch_discover_tests' from 'Catch.cmake'")
     ParseAndAddCatchTests_PrintDebugMessage("Started parsing ${TestTarget}")
     get_target_property(SourceFiles ${TestTarget} SOURCES)
     ParseAndAddCatchTests_PrintDebugMessage("Found the following sources: ${SourceFiles}")