Refactored Advanced PBR Terrain to use new for-loops (#1904)

* Refactored Advanced PBR Terrain to use new for-loops

Similar to my recent pull request doing the same for the base PbrTerrain shader (https://github.com/jMonkeyEngine/jmonkeyengine/pull/1901) this PR also adds for-loop support to the advanced version of the pbr shader that uses texture arrays

* Update PBRTerrain.frag

* Update AdvancedPBRTerrain.frag

jme3-terrain/src/main/resources/Common/MatDefs/Terrain/PBRTerrain.frag

@@ -2,7 +2,7 @@
 #import "Common/ShaderLib/PBR.glsllib"
 #import "Common/ShaderLib/Parallax.glsllib"
 #import "Common/ShaderLib/Lighting.glsllib"
-#import "MatDefs/ShaderLib/AfflictionLib.glsllib"
+#import "Common/MatDefs/Terrain/AfflictionLib.glsllib"
 
 varying vec3 wPosition;
 varying vec3 vNormal;