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/sk/common.json

@@ -686,6 +686,38 @@
     "recipient_name_placeholder": "Zobrazené meno",
     "autocomplete_search_server": "Hľadať na serveri",
     "autocomplete_searching": "Hľadanie...",
+    "toolbar": {
+      "bold": "Tučné",
+      "italic": "Kurzíva",
+      "underline": "Podčiarknuté",
+      "strikethrough": "Prečiarknuté",
+      "text_color": "Farba textu",
+      "remove_color": "Odstrániť farbu",
+      "heading_1": "Nadpis 1",
+      "heading_2": "Nadpis 2",
+      "bullet_list": "Odrážkový zoznam",
+      "ordered_list": "Číslovaný zoznam",
+      "quote": "Citát",
+      "code_block": "Blok kódu",
+      "align_left": "Zarovnať doľava",
+      "align_center": "Na stred",
+      "align_right": "Zarovnať doprava",
+      "text_direction": "Smer textu (RTL/LTR)",
+      "link": "Odkaz",
+      "table": "Tabuľka",
+      "clear_formatting": "Vymazať formátovanie",
+      "undo": "Späť",
+      "redo": "Znova",
+      "add_row_above": "Pridať riadok nad",
+      "add_row_below": "Pridať riadok pod",
+      "add_column_before": "Pridať stĺpec pred",
+      "add_column_after": "Pridať stĺpec za",
+      "delete_row": "Odstrániť riadok",
+      "delete_column": "Odstrániť stĺpec",
+      "toggle_header_row": "Prepnúť riadok záhlavia",
+      "delete_table": "Odstrániť tabuľku",
+      "pick_size": "Vybrať veľkosť"
+    },
     "send_filing_warning": "Odoslané - ale následné upratovanie zlyhalo, môže zostať zastaraný koncept."
   },
   "confirm_dialog": {