playground block: Add initial i18n support

[brandonpayton]

What?

This PR adds initial support for i18n.

I visually scanned PHP, TS, and TSX files and wrapped all the user-facing text I found with calls to __(). Because the Playground block is published under the slug interactive-code-block, that is the text domain used here.

There are a couple of tasks left:

• [ ] At least some of these need to be converted to _x() calls to add context for translators.
• [ ] There is a big block of HTML help text for "Mode" in edit.tsx that is not wrapped and needs more careful handling.

Testing Instructions

1. Check out this branch
2. Run the dev environment with nx run wordpress-playground-block:dev
3. Start a new post with localhost:8881/wp-admin/post-new.php
4. Insert a WordPress playground block
5. Enable the Code Editor in the block's settings and poke around in other ways to make sure there are no obvious problems with user facing text.

[brandonpayton]

Note: Any unrelated formatting changes are due to auto-formatting logic that runs on commit.

[brandonpayton]

This PR had grown stale and is now superceded by #327.