Improve ResourceLimits interface to be more forward compatible

New interface allows users to generate ResourceLimits for interface so
that additions to TBuiltInResource do not break the ABI.

Users should use the glslang-default-resource-limits library and the
Public/ResourceLimits.h header. Similar changes have been made to the
C interface. Use Public/resource_limits_c.h.

Fixes #2822

StandAlone/ResourceLimits.cpp

@@ -37,9 +37,9 @@
 #include <sstream>
 #include <cctype>
 
-#include "ResourceLimits.h"
+#include "glslang/Public/ResourceLimits.h"
 
-namespace glslang {
+TBuiltInResource Resources;
 
 const TBuiltInResource DefaultTBuiltInResource = {
     /* .MaxLights = */ 32,
@@ -529,4 +529,12 @@ void DecodeResourceLimits(TBuiltInResource* resources, char* config)
     }
 }
 
-}  // end namespace glslang
+TBuiltInResource* GetResources()
+{
+   return &Resources;
+}
+
+const TBuiltInResource* GetDefaultResources()
+{
+    return &DefaultTBuiltInResource;
+}