feat: implement theme customizer

frontend/app_flowy/packages/appflowy_editor/lib/l10n/intl_en.arb

@@ -0,0 +1,35 @@
+{
+  "@@locale": "en",
+  "bold": "Bold",
+  "@bold": {},
+  "bulletedList": "Bulleted List",
+  "@bulletedList": {},
+  "checkbox": "Checkbox",
+  "@checkbox": {},
+  "embedCode": "Embed Code",
+  "@embedCode": {},
+  "heading1": "H1",
+  "@heading1": {},
+  "heading2": "H2",
+  "@heading2": {},
+  "heading3": "H3",
+  "@heading3": {},
+  "highlight": "Highlight",
+  "@highlight": {},
+  "image": "Image",
+  "@image": {},
+  "italic": "Italic",
+  "@italic": {},
+  "link": "Link",
+  "@link": {},
+  "numberedList": "Numbered List",
+  "@numberedList": {},
+  "quote": "Quote",
+  "@quote": {},
+  "strikethrough": "Strikethrough",
+  "@strikethrough": {},
+  "text": "Text",
+  "@text": {},
+  "underline": "Underline",
+  "@underline": {}
+}