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/en/common.json

@@ -686,6 +686,38 @@
     "recipient_name_placeholder": "Display name",
     "autocomplete_search_server": "Search the server",
     "autocomplete_searching": "Searching...",
+    "toolbar": {
+      "bold": "Bold",
+      "italic": "Italic",
+      "underline": "Underline",
+      "strikethrough": "Strikethrough",
+      "text_color": "Text color",
+      "remove_color": "Remove color",
+      "heading_1": "Heading 1",
+      "heading_2": "Heading 2",
+      "bullet_list": "Bullet list",
+      "ordered_list": "Ordered list",
+      "quote": "Quote",
+      "code_block": "Code block",
+      "align_left": "Align left",
+      "align_center": "Align center",
+      "align_right": "Align right",
+      "text_direction": "Text direction (RTL/LTR)",
+      "link": "Link",
+      "table": "Table",
+      "clear_formatting": "Clear formatting",
+      "undo": "Undo",
+      "redo": "Redo",
+      "add_row_above": "Add row above",
+      "add_row_below": "Add row below",
+      "add_column_before": "Add column before",
+      "add_column_after": "Add column after",
+      "delete_row": "Delete row",
+      "delete_column": "Delete column",
+      "toggle_header_row": "Toggle header row",
+      "delete_table": "Delete table",
+      "pick_size": "Pick size"
+    },
     "send_filing_warning": "Sent - but the post-send cleanup failed, a stale draft may remain."
   },
   "confirm_dialog": {