i18n: localize the editor toolbar in all 23 locales

The rich-text editor was the last hardcoded-English surface in the
composer: 21 tooltip titles, the eight table-menu entries, the "Remove
color" entry and the table size picker's "Pick size" label were plain
strings while every other menu in the app is localized.

All of them now come from a new email_composer.toolbar namespace,
translated into all 23 locales using each platform's established
editor terminology (Word/Docs conventions - de "Formatierung löschen",
ar "مسح التنسيق", ja "書式をクリア", ...). The link prompt stays "URL",
which is the same term in every language.

Tooltips and self-sizing dropdowns have no width constraints, so longer
translations are safe everywhere.

locales/ar/common.json

@@ -686,6 +686,38 @@
     "recipient_name_placeholder": "الاسم المعروض",
     "autocomplete_search_server": "البحث في الخادم",
     "autocomplete_searching": "جارٍ البحث...",
+    "toolbar": {
+      "bold": "غامق",
+      "italic": "مائل",
+      "underline": "تسطير",
+      "strikethrough": "يتوسطه خط",
+      "text_color": "لون النص",
+      "remove_color": "إزالة اللون",
+      "heading_1": "عنوان 1",
+      "heading_2": "عنوان 2",
+      "bullet_list": "قائمة نقطية",
+      "ordered_list": "قائمة مرقمة",
+      "quote": "اقتباس",
+      "code_block": "كتلة برمجية",
+      "align_left": "محاذاة لليسار",
+      "align_center": "توسيط",
+      "align_right": "محاذاة لليمين",
+      "text_direction": "اتجاه النص (RTL/LTR)",
+      "link": "رابط",
+      "table": "جدول",
+      "clear_formatting": "مسح التنسيق",
+      "undo": "تراجع",
+      "redo": "إعادة",
+      "add_row_above": "إضافة صف بالأعلى",
+      "add_row_below": "إضافة صف بالأسفل",
+      "add_column_before": "إضافة عمود قبل",
+      "add_column_after": "إضافة عمود بعد",
+      "delete_row": "حذف الصف",
+      "delete_column": "حذف العمود",
+      "toggle_header_row": "تبديل صف الرأس",
+      "delete_table": "حذف الجدول",
+      "pick_size": "اختيار الحجم"
+    },
     "send_filing_warning": "تم الإرسال - لكن التنظيف بعد الإرسال فشل، وقد تبقى مسودة قديمة."
   },
   "confirm_dialog": {