Feat: Allow scrolling via keyboard in code blocks

[jhildenbiddle]

Summary

See title and original issue (below).

Related issue, if any:

#2224

What kind of change does this PR introduce?

Feature

For any code change:

• No documentation changes required
• No automated tests required

Note: These changes were tested and verified with the docsify-copy-code plugin.

Does this PR introduce a breaking change?

No

Tested in the following browsers:

• Chrome
• Firefox
• Safari
• Edge

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
docsify-preview	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 30, 2023 5:41am

[trusktr]

Can we see before/after videos?

[jhildenbiddle]

Can we see before/after videos?

Even better...

https://docsify-preview-git-2224-scrollable-code-docsifyjs.vercel.app/#/more-pages?id=sidebar

1. Click the "Sidebar" heading in the content area
2. Hit TAB three times so the focus is on code block.
   
   Note: Tab/focus behavior may be determined by your browser setting. For example, here are the settings for Safari 17:
   
3. Use the arrow keys to scroll right/left.

Now try the same thing on https://docsify.js.org/#/more-pages?id=sidebar:

1. Click the "Sidebar" heading in the content area
2. Hit TAB three times. Notice that it is not possible to focus on the code block, making it impossible to scroll the code block using the arrow keys.