feat(frontend): 投稿ウインドウにMFM要素を追加するボタンの追加 (#12788)

* functionPicker の追加

* Update CHANGELOG.md

* fix lint errors

* Add addMfmFunction

* add enableQuickAddMfmFunction setting

* Update CHANGELOG.md

issue 番号を追加

* Update index.d.ts

* change 'functionPicker' to 'mfmFunctionPicker'

* Change indent from 4 space to 1 tab

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Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>

locales/index.d.ts

@@ -1220,6 +1220,8 @@ export interface Locale {
     "overwriteContentConfirm": string;
     "seasonalScreenEffect": string;
     "decorate": string;
+    "addMfmFunction": string;
+    "enableQuickAddMfmFunction": string;
     "_announcement": {
         "forExistingUsers": string;
         "forExistingUsersDescription": string;