[render_vtk] Create a new mapper per actor

[sankhesh]

The vtkMapper is responsible for creating and uploading graphics resources per OpenGL context. Re-using vtkMapper instances across clones would cause unintentional side-effects like the ones described in #20002 and #21700 (comment)

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This change is 

[jwnimmer-tri]

@drake-jenkins-bot ok to test

+@SeanCurtis-TRI for discussion and/or review, please.

[SeanCurtis-TRI]

I'll get to this maybe today, definitely Monday. I can't say I'm surprised by the findings. My delay will give you a chance to address the CI woes.

[SeanCurtis-TRI]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: 1 unresolved discussion, LGTM missing from assignee SeanCurtis-TRI(platform), needs at least two assigned reviewers

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geometry/render_vtk/internal_render_engine_vtk.cc line 519 at r1 (raw file):

        vtkNew<vtkOpenGLPolyDataMapper> target_mapper;
        target_mapper->ShallowCopy(source_part.actor->GetMapper());
        target_actor->SetMapper(target_mapper);

I don't have permissions to push to your branch. So, instead of pushing a commit to resolve CI problems, I'll have to add the code here:

      for (const auto& source_part : source_prop.parts) {
        vtkNew<vtkActor> target_actor;
        target_actor->ShallowCopy(source_part.actor);
        vtkNew<vtkOpenGLPolyDataMapper> target_mapper;
        target_mapper->ShallowCopy(source_part.actor->GetMapper());
        target_actor->SetMapper(target_mapper);
        if (i == kDepth) {
          // The shallow copying doesn't fully reproduce the configuration of
          // depth shader.
          vtkOpenGLShaderProperty* shader_prop =
              vtkOpenGLShaderProperty::SafeDownCast(
                  target_actor->GetShaderProperty());
          DRAKE_DEMAND(shader_prop != nullptr);
          shader_prop->SetVertexShaderCode(render::shaders::kDepthVS);
          shader_prop->SetFragmentShaderCode(render::shaders::kDepthFS);
          target_mapper->AddObserver(vtkCommand::UpdateShaderEvent,
                                     uniform_setting_callback_.Get());
        }
        renderer.AddActor(target_actor);
        target_prop.parts.push_back(
            Part{.actor = std::move(target_actor), .T_GA = source_part.T_GA});
      }

Note: this is the same configuration work that is done in two other places: ImplementPolyData() and ImplementGltf(). This pushes us across the "rule of three" and it should be refactored for better re-use.

[sankhesh]

@SeanCurtis-TRI Thanks for the review. I should have prefaced this with WIP. It seems like drake copies the mapper by design

drake/geometry/render_vtk/internal_render_engine_vtk.h

Lines 297 to 298 in 9339312

	// Having "shared geometry" means having shared vtkPolyDataAlgorithm and
	// vtkOpenGLPolyDataMapper instances. The shader callback gets registered to

But that leads to graphics resources being copied and shared and unintentional side-effects. What was the original use-case for this?