Refactor Remote/LocalChange to have a single ChangeInfo

[7hong13]

What this PR does / why we need it?

Remote/LocalChange previously had a List<ChangeInfo>, but it has been changed to have a single ChangeInfo.

Any background context you want to provide?

What are the relevant tickets?

yorkie-team/yorkie-js-sdk#538

Fixes #

Checklist

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

[codecov]

Codecov Report

Merging #112 (2409f3a) into main (315ce1d) will increase coverage by 0.16%.
The diff coverage is 87.50%.

@@             Coverage Diff              @@
##               main     #112      +/-   ##
============================================
+ Coverage     80.13%   80.30%   +0.16%     
  Complexity      587      587              
============================================
  Files            53       53              
  Lines          2663     2660       -3     
  Branches        364      363       -1     
============================================
+ Hits           2134     2136       +2     
+ Misses          337      332       -5     
  Partials        192      192              

Impacted Files	Coverage Δ
yorkie/src/main/kotlin/dev/yorkie/core/Client.kt	77.62% <ø> (ø)
...ie/src/main/kotlin/dev/yorkie/document/Document.kt	69.92% <87.50%> (+3.01%)	⬆️