Revive planSnap() not to break downstream

[jslee02]

We will keep old function planSnap() for the downstream projects until they settled to the new planning API.

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Before creating a pull request

• Document new methods and classes
• Format code with make format

Before merging a pull request

• Set version target by selecting a milestone on the right side
• Summarize this change in CHANGELOG.md

[codecov]

Codecov Report

Merging #414 into master will decrease coverage by 0.1%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #414      +/-   ##
==========================================
- Coverage   79.57%   79.46%   -0.11%     
==========================================
  Files         230      231       +1     
  Lines        5944     5952       +8     
==========================================
  Hits         4730     4730              
- Misses       1214     1222       +8

Impacted Files	Coverage Δ
src/planner/SnapPlanner.cpp	0% <0%> (ø)