Add an OS.get_processor_name() method

This method can be used to get the CPU model name.
It can be used in conjunction with
`RenderingServer.get_video_adapter_name()` and
`RenderingServer.get_video_adapter_vendor()` for annotating benchmarks
and automatic graphics quality configuration.

core/os/os.cpp

@@ -358,6 +358,10 @@ int OS::get_processor_count() const {
 	return 1;
 }
 
+String OS::get_processor_name() const {
+	return "";
+}
+
 bool OS::can_use_threads() const {
 #ifdef NO_THREADS
 	return false;