refactor(frontend): frontend-embed/src/to-be-sharedを共通化

[kakkokari-gtyih]

What

書いてあるとおり

Why

Fix #14530

Additional info (optional)

Checklist

• [x] 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[bot]]

Codecov Report

Attention: Patch coverage is 36.45833% with 61 lines in your changes missing coverage. Please review.

Project coverage is 19.53%. Comparing base (f393b6b) to head (a9ec768). Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/ui/classic.vue	0.00%	3 Missing :warning:
...ackages/frontend/src/components/MkNoteDetailed.vue	0.00%	2 Missing :warning:
packages/frontend/src/store.ts	0.00%	2 Missing :warning:
packages/frontend/src/ui/universal.vue	0.00%	2 Missing :warning:
packages/frontend/src/boot/common.ts	0.00%	1 Missing :warning:
packages/frontend/src/boot/main-boot.ts	0.00%	1 Missing :warning:
...ckages/frontend/src/components/MkCropperDialog.vue	0.00%	1 Missing :warning:
packages/frontend/src/components/MkDonation.vue	0.00%	1 Missing :warning:
...s/frontend/src/components/MkEmbedCodeGenDialog.vue	0.00%	1 Missing :warning:
packages/frontend/src/components/MkPreview.vue	0.00%	1 Missing :warning:
... and 46 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #14536 +/- ## =========================================== - Coverage 19.57% 19.53% -0.05% =========================================== Files 717 713 -4 Lines 100466 100287 -179 Branches 1005 997 -8 =========================================== - Hits 19669 19591 -78 + Misses 80251 80152 -99 + Partials 546 544 -2 ```

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[syuilo]

🙏🏿