New proposal for Engine::Displayable

[nmellado]

• Please check if the PR fulfills these requirements

• [ ] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Be aware that the PR request cannot be accepted if it doesn't pass the Continuous Integration tests.

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Simplify API for Engine::Displayable and inheriting classes by using Core::MultiIndexGeometry.

• What is the current behavior? (You can also link to an open issue here) Mesh types are statically typed on Core Mesh types.

• What is the new behavior (if this is a feature change)? Take benefit of MultiIndexGeometry to allow dynamic typing of the rendered objects: Engine::GeometryDisplayable will store a collection of geometry layers. Expected API (right):

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) Will impact client code explicitly working with Engine::Displayable and inhering classes.

• Other information:

[codecov[bot]]

Codecov Report

Merging #802 (3598b89) into release-candidate (d77ca58) will increase coverage by 0.35%. The diff coverage is 48.11%.

:exclamation: Current head 3598b89 differs from pull request most recent head 076ec5e. Consider uploading reports for the commit 076ec5e to get more accurate results

@@                  Coverage Diff                  @@
##           release-candidate     #802      +/-   ##
=====================================================
+ Coverage              45.65%   46.01%   +0.35%     
=====================================================
  Files                    312      311       -1     
  Lines                  23060    23101      +41     
=====================================================
+ Hits                   10529    10630     +101     
+ Misses                 12531    12471      -60     

Impacted Files	Coverage Δ
src/Core/Animation/LinearBlendSkinning.cpp	0.00% <ø> (ø)
src/Core/Geometry/AbstractGeometry.hpp	66.66% <ø> (ø)
src/Core/Geometry/MeshPrimitives.cpp	33.78% <0.00%> (-1.92%)	:arrow_down:
src/Core/Geometry/MeshPrimitives.hpp	0.00% <ø> (ø)
src/Core/Geometry/TriangleMesh.hpp	80.16% <ø> (ø)
src/Engine/Rendering/ForwardRenderer.cpp	52.28% <0.00%> (+0.01%)	:arrow_up:
src/Engine/Scene/SkinningComponent.cpp	0.00% <0.00%> (ø)
src/Engine/Scene/SkinningComponent.hpp	0.00% <ø> (ø)
src/Engine/Data/Mesh.hpp	55.10% <20.00%> (-14.61%)	:arrow_down:
src/Core/Geometry/IndexedGeometry.hpp	65.25% <39.28%> (-5.86%)	:arrow_down:
... and 5 more

... and 2 files with indirect coverage changes

[dlyr]

note for futur skinning https://cims.nyu.edu/gcl/papers/EG2014-Lighting.pdf