[EuiIcon] Add keyboard glyph

[elizabetdev]

Summary

This PR adds a keyboard glyph to EuiIcon. This icon is required to finish #6036. We could use the icon keyboardShortcut but as we can see from the screenshots on #6036 it's hard to tell what the icon does just looking at it. That's why we decide to create a new icon.

I tried different designs that can be found here: Figma

I run multiple tests in Figma to see how this icon would look in a EuiDataGrid. The prototype can be found here: Figma prototype.

After that, I showed the prototype to @chandlerprall and @constancecchen and both of them picked option 6. I run more tests and this icon didn't work out for non-retina displays (IMO). It gets blurry because the circles are not in the grid and they are not 1px but 1.5px.

So I went back to design and this time I focused on an icon that would work for non-retina displays. From all the tests option 8 worked the best and that's the option I'm adding to EUI.

Final Design

Final design light and dark theme

Deprecation of keyboardShortcut in favor of keyboard

Because the new icon keyboard is more generic we're deprecating the icon keyboardShortcut in favor of the new one. I asked @ryankeairns about his opinion (#6058 (comment)) and we're on the same page.

I searched all Elastic usages of the keyboardShortcut icon and only found the following one: https://github.com/elastic/kibana/blob/f990f31023784f71dde3bb8a74ba52c9c60bbf69/x-pack/plugins/canvas/public/components/help_menu/help_menu.component.tsx#L55

I created a mock in Figma to show how the new icon would look in Kibana. I also replaced one icon usage in our EUI docs.

Checklist

• Checked in both light and dark modes
• Checked in mobile
• Checked in Chrome, Safari, Edge, and Firefox
• Props have proper autodocs and playground toggles
• Added documentation
• Checked Code Sandbox works for any docs examples
• Added or updated jest and cypress tests
• Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• Updated the Figma library counterpart
• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_6058/

[ryankeairns]

This is looking good. I would suggest we not keep both and, instead, just go with the new version. Using the name keyboard seems to best align to our preference toward literal names as to not suggest a particular use case.

I don't suspect there are many instances of keyboardShortcut in use in our own product UIs, but this would break others. In either case, the actual fix is about as easy they come.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_6058/

[cee-chen]

🎉 🎉 🎉 Thanks for your awesome work on this Elizabet!! I love the new icon, and think it's super clear!