refactor: replace deprecated 'keyCode' with 'key' in key event handling

[R1shabh-Gupta]

Trac ticket: https://core.trac.wordpress.org/ticket/63759

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[R1shabh-Gupta]

There are multiple files that require replacing event.keyCode with event.key. I realized that combining all changes into a single PR would result in too many file modifications, making it difficult to review and test effectively.
To keep things manageable, I’ve decided to create separate PRs for each set of changes.

I’m closing this PR for now. Please let me know if you have any concerns or suggestions.

[joedolson]

I think that makes sense. The logical thing is probably to transform the ticket into a task and add smaller tickets to progress towards completion.