[GPU] Vulkan fragment shader interlock RB and related fixes/cleanup

Also fixes addressing of MSAA samples 2 and 3 for 64bpp color render targets in the ROV RB implementation on Direct3D 12.
Additionally, with FSI/ROV, alpha test and alpha to coverage are done only if the render target 0 was dynamically written to (according to the Direct3D 9 rules for writing to color render targets, though not sure if they actually apply to the alpha tests on Direct3D 9, but for safety).
There is also some code cleanup for things spotted during the development of the feature.

tools/shader-playground/Editor.Designer.cs

@@ -191,9 +191,10 @@
       this.translationComboBox.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList;
       this.translationComboBox.FormattingEnabled = true;
       this.translationComboBox.Items.AddRange(new object[] {
-            "DXBC (RTV/DSV RB)",
-            "DXBC (ROV RB)",
-            "SPIR-V"});
+            "DXBC (render target RB)",
+            "DXBC (rasterizer-ordered view RB)",
+            "SPIR-V (framebuffer RB)",
+            "SPIR-V (fragment shader interlock RB)"});
       this.translationComboBox.Location = new System.Drawing.Point(1224, 0);
       this.translationComboBox.Margin = new System.Windows.Forms.Padding(3, 0, 3, 0);
       this.translationComboBox.Name = "translationComboBox";

tools/shader-playground/Editor.cs

@@ -235,6 +235,7 @@ namespace shader_playground {
           outputType = "dxbctext";
           break;
         case 2:
+        case 3:
           outputType = "spirvtext";
           break;
       }
@@ -269,8 +270,9 @@ namespace shader_playground {
         "--vertex_shader_output_type=" + vertexShaderType,
         "--dxbc_source_map=true",
       };
-      if (translationComboBox.SelectedIndex == 1) {
-        startArguments.Add("--shader_output_dxbc_rov=true");
+      if (translationComboBox.SelectedIndex == 1 ||
+          translationComboBox.SelectedIndex == 3) {
+        startArguments.Add("--shader_output_pixel_shader_interlock=true");
       }
 
       startInfo = new ProcessStartInfo(compilerPath_);