Consider vtkCompositePolyDataMpper in GetMTime for batched polydata mapper

- closes vtk/vtk#19395
- without it, the batched polydata mappers would not update the buffers even when the composite data display attributes may have been modified due to a scalar visibility setting change.
- the desktop mapper worked because it's `GetNeedToRebuildBufferObjects` indirectly compared the number of polydata in the current batch and previously rendered batch. This happened in `vtkStateStorage::operator !=()`. When the last block's scalar visibility was toggled from off to on, it recognized that the batch size has changed and uploaded the new batch of polydata.
- the wasm mapper did not because it's `IsUptoDate` did not know about batch size and returned true even when the composite data display attributes were modified.
- the fix could record the number of polydata in a batch and compare the number of polydata in `IsDataObjectUptoDate` with the last render. However, a better fix is to consider the MTime of the parent `vtkCompositePolyDataMapper` (that also considers the MTime of `vtkCompositeDataDisplayAttributes`) as the MTime concept was meant to fulfill this kind of state tracking need.

Rendering/OpenGL2/vtkOpenGLBatchedPolyDataMapper.cxx

@@ -1384,4 +1384,15 @@ int vtkOpenGLBatchedPolyDataMapper::CanUseTextureMapForColoring(vtkDataObject*)
   return 1;
 }
 
+vtkMTimeType vtkOpenGLBatchedPolyDataMapper::GetMTime()
+{
+  if (this->Parent)
+  {
+    return std::max(this->Superclass::GetMTime(), this->Parent->GetMTime());
+  }
+  else
+  {
+    return this->Superclass::GetMTime();
+  }
+}
 VTK_ABI_NAMESPACE_END

Rendering/OpenGL2/vtkOpenGLBatchedPolyDataMapper.h

@@ -72,6 +72,11 @@ public:
   virtual void ProcessCompositePixelBuffers(vtkHardwareSelector* sel, vtkProp* prop,
     GLBatchElement* glBatchElement, std::vector<unsigned int>& mypixels);
 
+  /**
+   * Returns the maximum of our and Parent vtkCompositePolyDataMapper's MTime
+   */
+  vtkMTimeType GetMTime() override;
+
 protected:
   vtkOpenGLBatchedPolyDataMapper();
   ~vtkOpenGLBatchedPolyDataMapper() override;

Rendering/OpenGL2/vtkOpenGLLowMemoryBatchedPolyDataMapper.cxx

@@ -932,4 +932,15 @@ int vtkOpenGLLowMemoryBatchedPolyDataMapper::CanUseTextureMapForColoring(vtkData
   return 1;
 }
 
+vtkMTimeType vtkOpenGLLowMemoryBatchedPolyDataMapper::GetMTime()
+{
+  if (this->Parent)
+  {
+    return std::max(this->Superclass::GetMTime(), this->Parent->GetMTime());
+  }
+  else
+  {
+    return this->Superclass::GetMTime();
+  }
+}
 VTK_ABI_NAMESPACE_END

Rendering/OpenGL2/vtkOpenGLLowMemoryBatchedPolyDataMapper.h

@@ -74,6 +74,11 @@ public:
   virtual void ProcessCompositePixelBuffers(vtkHardwareSelector* sel, vtkProp* prop,
     GLBatchElement* glBatchElement, std::vector<unsigned int>& mypixels);
 
+  /**
+   * Returns the maximum of our and Parent vtkCompositePolyDataMapper's MTime
+   */
+  vtkMTimeType GetMTime() override;
+
 protected:
   vtkOpenGLLowMemoryBatchedPolyDataMapper();
   ~vtkOpenGLLowMemoryBatchedPolyDataMapper() override;