Playground improvements for SPIKE Prime

[cwillisf]

Proposed Changes

• Move the playground from scratch-link/playground.html to scratch-link/playground/playground.html
• Split the playground into multiple files (one HTML file containing no JS along with several JS files)
• Refactor BLE features to make some of them available for BT as well
• Make BT features more flexible (don't assume EV3)
  • Move EV3 features to EV3-specific buttons
  • Allow omitting or overriding the PIN
  • Remove hard-coded peripheral ID and instead auto-fill peripheral ID on discovery
  • Add "name" and "namePrefix" boxes for upcoming Scratch Link feature
• Allow user to collapse any fieldset by clicking its label (HTML <legend> element)
• Add a button to clear the log
• Improve display of objects in the log

Reason for Changes

The Bluetooth Classic (BT) section of the playground had fallen behind the BLE section, and was basically only useful for the EV3. This brings BT up to the same level as BLE and hopefully will make it easier to maintain them both (and keep them in sync) going forward.

[knandersen]

@cwillisf I tried pulling the PR. I just need to open the playground.html right? no need for a server or anything? If I click Discover peripherals I get an error:

Button btDiscover caught exception: TypeError {stack: "btDiscover@file:///Users/dkkevian/Dev/scratch-link/playground/playground.js:391:15↵file:///Users/dkkevian/Dev/scratch-link/playground/playground.js:11:17"})