ATOM-14688 Disable Individual Layers

Added new test cases for disabling individual StandardMultilayerPBR layers.

Scripts/ExpectedScreenshots/StandardMultilayerPBR/001_manyfeatures_layer2off.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:e44e6c4dbe2b09ba31e1059c23c38a0e321fc3410d392a27606efdd9cec5601a
+size 1435801

Scripts/ExpectedScreenshots/StandardMultilayerPBR/001_manyfeatures_layer3off.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:f41ace3710a2be002a24e042a1cb4ee86ae52ba32cca10228d2a2b11b2d1983b
+size 1456824

Scripts/MaterialScreenshotTests.bv.lua

@@ -158,6 +158,8 @@ g_screenshotOutputFolder = ResolvePath('@user@/Scripts/Screenshots/StandardMulti
 Print('Saving screenshots to ' .. NormalizePath(g_screenshotOutputFolder))
 
 GenerateMaterialScreenshot('Level I', '001_ManyFeatures', {model=g_cubeModel, cameraHeading=-125.0, cameraPitch=-16.0, cameraZ=0.12})
+GenerateMaterialScreenshot('Level I', '001_ManyFeatures_Layer2Off', {model=g_cubeModel, cameraHeading=-125.0, cameraPitch=-16.0, cameraZ=0.12})
+GenerateMaterialScreenshot('Level I', '001_ManyFeatures_Layer3Off', {model=g_cubeModel, cameraHeading=-125.0, cameraPitch=-16.0, cameraZ=0.12})
 GenerateMaterialScreenshot('Level I', '002_ParallaxPdo', {model=g_cubeModel, cameraHeading=15.0, cameraPitch=28.0, lighting="Goegap (Alt)"})
 GenerateMaterialScreenshot('Level G', '003_Debug_BlendSource', {model=g_cubeModel})
 GenerateMaterialScreenshot('Level F', '003_Debug_DepthMaps', {model=g_cubeModel})