rhi: Add the wgsl enum value for shaders

There is no clear path to generating WGSL shaders, but that
should not prevent QShader from being able to contain such
shaders.

Change-Id: I819e1c67c38d675971907a3a80885ddec78da0f6
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/rhi/qshader.cpp

@@ -160,6 +160,7 @@ QT_BEGIN_NAMESPACE
     \value MslShader Metal Shading Language
     \value DxilShader Direct3D bytecode (HLSL compiled by \c dxc)
     \value MetalLibShader Pre-compiled Metal bytecode
+    \value WgslShader WGSL
  */
 
 /*!

src/gui/rhi/qshader_p.h

@@ -98,7 +98,8 @@ public:
         DxbcShader, // fxc
         MslShader,
         DxilShader, // dxc
-        MetalLibShader // xcrun metal + xcrun metallib
+        MetalLibShader, // xcrun metal + xcrun metallib
+        WgslShader
     };
 
     enum Variant {