enhance(frontend): テキストエリアのサイズを自動で調整するように

[kakkokari-gtyih]

What

かいてあるとおり

テスト中

Why

Fix #15234

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

❌ Patch coverage is 14.28571% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 14.92%. Comparing base (8a85ee1) to head (39a021d).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/directives/autosize.ts	15.38%	9 Missing and 2 partials ⚠️
packages/frontend/src/components/MkPostForm.vue	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #17337      +/-   ##
===========================================
- Coverage    24.89%   14.92%   -9.98%     
===========================================
  Files         1150      243     -907     
  Lines        38825    11879   -26946     
  Branches     10774     4021    -6753     
===========================================
- Hits          9667     1773    -7894     
+ Misses       23393     7940   -15453     
+ Partials      5765     2166    -3599     

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