Add TextureViewer.GetChannelVisibility that returns a tuple

* This is more natural to access and use from python. The old function could
  probably be removed but since we also changed the name we'll keep it.

qrenderdoc/Code/Interface/QRDInterface.h

@@ -891,6 +891,13 @@ etc.
 )");
   virtual uint32_t GetChannelVisibilityBits() = 0;
 
+  DOCUMENT(R"(Return which channels are currently displayed, as a four-component tuple.
+
+:return: The current channel visibility per component.
+:rtype: Tuple[bool,bool,bool,bool]
+)");
+  virtual rdcfixedarray<bool, 4> GetChannelVisibility() = 0;
+
   DOCUMENT(R"(Set the visibility of each channel.
 
 :param bool red: Whether the red channel should be visible.

qrenderdoc/Code/pyrenderdoc/PythonInvokers.cpp

@@ -981,6 +981,10 @@ struct ITextureViewerInvoker : UIThreadInvoker<ITextureViewer>
   {
     return InvokeRetFunction<uint32_t>(&ITextureViewer::GetChannelVisibilityBits);
   }
+  rdcfixedarray<bool, 4> GetChannelVisibility()
+  {
+    return InvokeRetFunction<rdcfixedarray<bool, 4>>(&ITextureViewer::GetChannelVisibility);
+  }
   void SetChannelVisibility(bool red, bool green, bool blue, bool alpha)
   {
     return InvokeVoidFunction(&ITextureViewer::SetChannelVisibility, red, green, blue, alpha);