Singleton

[dlyr]

• Please check if the PR fulfills these requirements
• [ ] The commit message follows our guidelines
• [x] 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, ...) Use unique_ptr as singleton instance

• What is the current behavior? (You can also link to an open issue here) Singleton use raw ptr

• What is the new behavior (if this is a feature change)? Using unique_ptr prevent from missing destroyInstance, and make clang-tidy happier.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) Maybe related to the use of awkward unique_ptr to singleton instance (which make the unique_ptr owner virtually the owner of the singleton instance and can arise spurious singleton delete).

• Other information: need to be tested, maybe simply remove class member singleton views. Or use shared_ptr/weak_ptr, or reference_wrapper, as introduce here #996

[codecov[bot]]

Codecov Report

Merging #997 (65f7607) into release-candidate (f530ebf) will decrease coverage by 0.01%. The diff coverage is 25.00%.

:exclamation: Current head 65f7607 differs from pull request most recent head 6a2680a. Consider uploading reports for the commit 6a2680a to get more accurate results

@@                  Coverage Diff                  @@
##           release-candidate     #997      +/-   ##
=====================================================
- Coverage              42.07%   42.06%   -0.02%     
=====================================================
  Files                    341      341              
  Lines                  22579    22574       -5     
=====================================================
- Hits                    9500     9495       -5     
  Misses                 13079    13079              

Impacted Files	Coverage Δ
src/Engine/RadiumEngine.hpp	100.00% <ø> (ø)
src/Gui/BaseApplication.cpp	0.00% <0.00%> (ø)
src/Gui/BaseApplication.hpp	0.00% <ø> (ø)
src/Headless/CLIViewer.cpp	56.52% <100.00%> (-0.38%)	:arrow_down:
src/Engine/Scene/SystemDisplay.cpp	23.07% <0.00%> (-5.50%)	:arrow_down:
src/Engine/Scene/ComponentMessenger.cpp	90.90% <0.00%> (-0.76%)	:arrow_down:
src/Engine/RadiumEngine.cpp	63.48% <0.00%> (-0.16%)	:arrow_down:
src/Gui/Utils/KeyMappingManager.cpp	76.73% <0.00%> (-0.07%)	:arrow_down:
src/Engine/Rendering/DebugRender.cpp	25.98% <0.00%> (+0.20%)	:arrow_up:

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[nmellado]

@dlyr to you want to clean the history before merging ? (fine for me as it is now)