Canvas: Added keyboard shortcuts for styling and comments

✨ Minor updates

Added support for text underline styles

Added keyboard shortcuts for the following actions (Mac / Windows):

⌘+E / Ctrl+E: toggle code style at selection

⌘+K / Ctrl+K: toggle link annotation at selection

⌘+U / Ctrl+U: toggle underline style at selection

Shift+⌘+M / Shift+Control+M: create comment at selection

⌘+X / Shift+Control+X: toggle strikethrough style at selection