refactor: improve the content area width of the editor for low-resolution screens

[ruibaby]

What type of PR is this?

/area ui
/area editor
/kind improvement
/milestone 2.17.x

What this PR does / why we need it:

优化文章编辑器内容区域在低分屏下的表现。

默认：

小屏幕：

Which issue(s) this PR fixes:

Fixes #6172

Special notes for your reviewer:

建议测试在各个屏幕下的表现。

Does this PR introduce a user-facing change?

优化文章编辑器内容区域在低分屏下的表现。

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.92%. Comparing base (bc10336) to head (b79b936).
Report is 13 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6175      +/-   ##
============================================
+ Coverage     54.51%   56.92%   +2.41%     
- Complexity     3523     3704     +181     
============================================
  Files           646      652       +6     
  Lines         21862    22038     +176     
  Branches       1528     1537       +9     
============================================
+ Hits          11917    12546     +629     
+ Misses         9328     8886     -442     
+ Partials        617      606      -11     

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[JohnNiang]

/approve

[LIlGG]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JohnNiang, LIlGG

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• ui/OWNERS [JohnNiang]

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