Add ShaderLab language (#3490)

* Add ShaderLab language

* Update HLSL and ShaderLab grammars to latest version

* Add .shader extension back to GLSL language

* Add sample GLSL .shader files

Note that these are copies of existing GLSL samples, renamed to have
the .shader extension.

lib/linguist/languages.yml

@@ -4014,6 +4014,13 @@ Self:
   tm_scope: none
   ace_mode: text
   language_id: 345
+ShaderLab:
+  type: programming
+  extensions:
+  - ".shader"
+  ace_mode: text
+  tm_scope: source.shaderlab
+  language_id: 664257356
 Shell:
   type: programming
   color: "#89e051"