Add depth rendering mode

[jslee02]

Usage:

auto viewer = dart::gui::osg::Viewer();
viewer.setCameraMode(dart::gui::osg::CameraMode::DEPTH);  // or dart::gui::osg::CameraMode::RGBA (default)

RGBA mode:

Depth mode

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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
• Add Python bindings for new methods and classes

[codecov]

Codecov Report

Merging #1652 (ea604f9) into main (90712b1) will increase coverage by 0.01%.
The diff coverage is 26.47%.

❗ Current head ea604f9 differs from pull request most recent head 4f84694. Consider uploading reports for the commit 4f84694 to get more accurate results

@@            Coverage Diff             @@
##             main    #1652      +/-   ##
==========================================
+ Coverage   59.14%   59.15%   +0.01%     
==========================================
  Files         499      499              
  Lines       40911    40915       +4     
==========================================
+ Hits        24195    24202       +7     
+ Misses      16716    16713       -3     

Impacted Files	Coverage Δ
python/dartpy/gui/osg/ImGuiViewer.cpp	64.28% <0.00%> (ø)
python/dartpy/gui/osg/Viewer.cpp	59.06% <27.27%> (+1.39%)	⬆️
dart/collision/detail/UnorderedPairs.hpp	95.00% <0.00%> (+5.00%)	⬆️