aria-keyshortcuts should use AltGraph instead of Option

[compulim]

Screenshots

Version

main of 4.15.3-0

Describe the bug

According to W3C, aria-keyshortcuts should be "alt+shift+a" or "ctrl+altgraph+a" (for "Ctrl + Option + A" in macOS)

However, when narrating it as accessible name, we do not need + (plus) signs.

Keystroke	aria-keyshortcuts	Accessible name
Alt + Shift + A	"Alt+Shift+a"	"Alt Shift A"
Ctrl + Option + A	"Ctrl+AltGraph+a"	"Ctrl Option A"

Steps to reproduce

1. Send suggested-actions to the bot
2. Observe the <button> element of suggested action button

Expected behavior

It should have aria-keyshortcuts of "alt+shift+a".

Additional context

[Bug]