Fix incorrect calculation in indexTree.treePosToPath operation

[raararaara]

What this PR does / why we need it:

This patch addresses an issue arising from the tree.edit operation in response to problem with calculating the fromPath when multiple treePos represent a single index-based coordinate, leading to inaccuracies.

This PR contains migration work for yorkie-team/yorkie-js-sdk#751, so detailed information can also be found there.

Which issue(s) this PR fixes:

Address #749
Related yorkie-team/yorkie-js-sdk#751

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Attention: Patch coverage is 25.92593% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 50.62%. Comparing base (0987cbc) to head (4bf60b9).
Report is 2 commits behind head on main.

Files	Patch %	Lines
pkg/index/tree.go	31.25%	9 Missing and 2 partials ⚠️
pkg/document/crdt/tree.go	18.18%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #824      +/-   ##
==========================================
- Coverage   50.71%   50.62%   -0.10%     
==========================================
  Files          70       70              
  Lines       10213    10234      +21     
==========================================
+ Hits         5180     5181       +1     
- Misses       4512     4530      +18     
- Partials      521      523       +2     

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[hackerwins]

Thanks for your contribution.
I left simple comments.

[hackerwins]

LGTM.