[logging] Ensure that glib logging goes through the new logging mechanics and that...

[logging] Ensure that glib logging goes through the new logging mechanics and that the domain prefix is preserved.

Call g_log_set_default_handler in mono_trace_set_log_handler and mono_trace_set_log_handler_internal to ensure that g_ logging is properly routed.

Additionally, change the internal logging callback to take the log message as a single string to simplify things.