Align writing of generated Slang shaders with GLSL (#2698)

This brings GenSlang tests to be in line with GenGlsl, and disables the writing of tested shaders to disk.

The main motivation is that the tests (both Slang and GLSL) actually currently produce invalid code for the `NG_lightcompoundtest` node, which is confusing.

Author: tdavidovicNV

source/MaterialXTest/MaterialXGenSlang/GenSlang.cpp

@@ -151,7 +151,7 @@ TEST_CASE("GenShader: Slang Shader Generation", "[genslang]")
     generator = mx::SlangShaderGenerator::create();
 
     const mx::FilePath logPath("genslang_generate_test.txt");
-    SlangShaderGeneratorTester tester(generator, testRootPaths, searchPath, logPath, true);
+    SlangShaderGeneratorTester tester(generator, testRootPaths, searchPath, logPath, false);
 
     // Handle resource binding layouts if requested.
     const mx::GenOptions genOptions;

source/MaterialXTest/MaterialXGenSlang/GenSlang.h

@@ -34,6 +34,7 @@ class SlangShaderGeneratorTester : public GenShaderUtil::ShaderGeneratorTester
     {
         _skipNodeDefs.insert("ND_displacement_float");
         _skipNodeDefs.insert("ND_displacement_vector3");
+        _skipNodeDefs.insert("ND_lightcompoundtest");
         ParentClass::addSkipNodeDefs();
     }