Add World::create()

[jslee02]

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Before creating a pull request

• Document new methods and classes

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 #962 into release-6.4 will increase coverage by <.01%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##           release-6.4     #962      +/-   ##
===============================================
+ Coverage        56.63%   56.64%   +<.01%     
===============================================
  Files              310      310              
  Lines            23921    23923       +2     
===============================================
+ Hits             13548    13550       +2     
  Misses           10373    10373

Impacted Files	Coverage Δ
dart/utils/sdf/SdfParser.cpp	65.87% <100%> (ø)	⬆️
dart/simulation/World.cpp	71.79% <100%> (+0.2%)	⬆️
dart/utils/urdf/DartLoader.cpp	74.38% <100%> (ø)	⬆️
dart/utils/SkelParser.cpp	69.74% <100%> (ø)	⬆️