Diagnostics: Fix demangling (#1215)

Rename to better names
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dCommon/Demangler.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <string>
+
+namespace Demangler {
+	// Given a char* containing a mangled name, return a std::string containing the demangled name.
+	// If the function fails for any reason, it returns an empty string.
+	std::string Demangle(const char* name);
+}