Fix missing escapeString in Tree Marshal

[chacha912]

What this PR does / why we need it:

This PR addresses the issue of missing escape string processing in Tree Marshal. The absence of this processing causes errors in the dashboard when accessing a document containing special characters in Tree data type.

Which issue(s) this PR fixes:

Fixes https://github.com/yorkie-team/dashboard/issues/139 Related https://github.com/yorkie-team/yorkie-js-sdk/pull/700

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 50.95%. Comparing base (f3231c2) to head (2a8db00).

:exclamation: Current head 2a8db00 differs from pull request most recent head 80b0097. Consider uploading reports for the commit 80b0097 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #830 +/- ## ========================================== + Coverage 50.81% 50.95% +0.14% ========================================== Files 70 70 Lines 10226 10226 ========================================== + Hits 5196 5211 +15 + Misses 4504 4487 -17 - Partials 526 528 +2 ```

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