fix: playground test blocks, text area listeners, and show/hide buttons

[BeksOmega]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide
• I ran npm run format and npm run lint

The details

Resolves

N/A

Proposed Changes

Makes it so that:

1. Test blocks are accessible.
2. The text area properly triggers updates.
3. The show and hide buttons work.

Behavior Before Change

None of those things worked.

Behavior After Change

Now they work!

Reason for Changes

Need to be able to use the playground for testing.

Test Coverage

Tested on:

• Desktop Chrome

Documentation

N/A

Additional Information

Abby figured out how to get the test blocks to import! They need to be added as a plain script instead of a module script (I think b/c we're using the dist version). I didn't think that would work b/c Blockly wouldn't be defined. But it turns out prepare.js defines Blockly in the global scope. So as long as we load the test blocks after we load prepare.js everything is happy :D