Handle concurrent editing and styling in Tree

[raararaara]

What this PR does / why we need it?

Handle concurrent editing and styling in Tree

We will use maxCreatedAtMapByActor until the introduction of
VersionVector. yorkie-team/yorkie#800

Any background context you want to provide?

What are the relevant tickets?

Related yorkie-team/yorkie#854

Checklist

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

[codecov]

Codecov Report

Attention: Patch coverage is 93.87755% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 80.68%. Comparing base (ba635e6) to head (7dc48e5).

Files	Patch %	Lines
src/document/crdt/tree.ts	90.90%	0 Missing and 2 partials ⚠️
src/document/crdt/rga_tree_split.ts	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #803      +/-   ##
==========================================
+ Coverage   80.50%   80.68%   +0.17%     
==========================================
  Files          59       59              
  Lines        4448     4468      +20     
  Branches      901      906       +5     
==========================================
+ Hits         3581     3605      +24     
+ Misses        605      601       -4     
  Partials      262      262              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[hackerwins]

💪

[hackerwins]

Thanks for your contribution.