Reworks the $Core::commonShaderPath variable usage to be a static variable in ShaderGen for efficiency(only one getVariable when shadergen is initialized), as well as implements the ability to set a default value, and ensures that it tries to set a path even if the pref variable is missing which is important for ported projects from older builds.

Engine/source/shaderGen/shaderGen.h

@@ -47,7 +47,6 @@
 #include "materials/materialFeatureData.h"
 #endif
 
-
 /// Base class used by shaderGen to be API agnostic.  Subclasses implement the various methods
 /// in an API specific way.
 class ShaderGenPrinter
@@ -165,6 +164,8 @@ public:
    void setComponentFactory(ShaderGenComponentFactory* factory) { mComponentFactory = factory; }
    void setFileEnding(String ending) { mFileEnding = ending; }
 
+   static String smCommonShaderPath;
+
 protected:   
 
    friend class ManagedSingleton<ShaderGen>;