Convert shortcode package to TypeScript

[mikeybinns]

What?

Converting the shortcodes package to TypeScript.

Why?

It's an enhancement, while not necessary it is helpful to reduce bugs in both the code of the package and end users code if they consume types.

How?

• All JS files converted to TypeScript
• Changed object.assign to JS Class declaration for clarity.
• Removed attrs method from shortcode class as it was inaccessible due to a property of the same name. attrs function is still exported separately as before.
• Types exported from package.json
• I fixed a bug in the implementation of the shortcode class where valid attribute objects were treated as shallow objects.
• Add a few extra automated tests to cover that bug

Testing Instructions

Covered by automatic tests.

Testing Instructions for Keyboard

N/A

Screenshots or screencast

N/A

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: mikeybinns <mikeybinns@git.wordpress.org>
Co-authored-by: manzoorwanijk <manzoorwanijk@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[manzoorwanijk]

We can close or redo this following #67416.

CC @gziolo

[mikeybinns]

Happy to close mine :)

[gziolo]

Nice! It’s exactly what needs to happen next. We definitely need to refresh this PR. @mikeybinns, will you have time to rebase this branch with trunk or is it fine to open another branch based on the existing code?

[gziolo]

Ok, good. We definitely want to reuse all the new tests introduced in addition to other changes proposed ❤️

[mikeybinns]

Okay, in that case, I will rebase it when I have time :)