UX: More consistent shortcut labels for macOS (PR #14538)

We previously showed macOS/iOS glyphs for the composer toolbar buttons only. This uses them for the composer Submit button tooltip and on the keyboard shortcuts modal.

I left Shift and Ctrl untouched on the keyboard shortcuts modal. This is a little inconsistent, but Shift and Ctrl are easier to read and macOS keyboards very often don’t have icons for the Shift key, i.e.: Magic Keyboard with Touch ID for Mac models with Apple silicon - US English - Apple


I like it!