Fix depth testing for transparent objects

[jslee02]

Summary:
This PR fixes the issue that a transparent object is sometimes not displayed when it's behind another transparent object, which is not captured by #1414. It's fixed by two changes. Firstly, set OSG to render transparent objects after opaque objects using setRenderingHint() (see: this post). Secondly, disable z-buffer writing while enabling z-buffer testing during drawing transparent objects so transparent objects don't get rendered when they're behind opaque object but always rendered (with blending) even when they're overlapped with other transparent objects regardless of their z-depths. See this post.

Not fixed by this PR:
Fixing for VoxelShape is saved for the future PR. Also, there could be performance hit for MeshShape when the color mode is COLOR_INDEX.

Before the fix:

After the fix:

---

Before creating a pull request

• Document new methods and classes
• Format new code files using ClangFormat by running make format
• Build with -DDART_TREAT_WARNINGS_AS_ERRORS=ON and resolve all the compile warnings

Before merging a pull request

• Set version target by selecting a milestone on the right side
• Summarize this change in CHANGELOG.md
• Add unit test(s) for this change

[codecov]

Codecov Report

Merging #1643 (55aad10) into main (0bbc551) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 55aad10 differs from pull request most recent head c4b4484. Consider uploading reports for the commit c4b4484 to get more accurate results

@@            Coverage Diff             @@
##             main    #1643      +/-   ##
==========================================
- Coverage   59.09%   59.08%   -0.01%     
==========================================
  Files         491      491              
  Lines       40555    40555              
==========================================
- Hits        23965    23962       -3     
- Misses      16590    16593       +3     

Impacted Files	Coverage Δ
dart/dynamics/Skeleton.cpp	67.74% <0.00%> (-0.17%)	⬇️