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);

qrenderdoc/Windows/TextureViewer.cpp

@@ -2294,6 +2294,11 @@ uint32_t TextureViewer::GetChannelVisibilityBits()
   return ret;
 }
 
+rdcfixedarray<bool, 4> TextureViewer::GetChannelVisibility()
+{
+  return {m_TexDisplay.red, m_TexDisplay.green, m_TexDisplay.blue, m_TexDisplay.alpha};
+}
+
 void TextureViewer::SetChannelVisibility(bool red, bool green, bool blue, bool alpha)
 {
   ui->channelRed->setChecked(red);

qrenderdoc/Windows/TextureViewer.h

@@ -155,6 +155,7 @@ public:
   void SetHistogramRange(float blackpoint, float whitepoint) override;
 
   uint32_t GetChannelVisibilityBits() override;
+  rdcfixedarray<bool, 4> GetChannelVisibility() override;
   void SetChannelVisibility(bool red, bool green, bool blue, bool alpha) override;
 
   // ICaptureViewer