Update to Go 1.20 and React with line numbers

[grantnelson-wf]

I'm doing a lot of experimentation and improvements to the GopherJS playground.

• Updated the README.md
• Added an icon
• Adding CI to address Add some sort of CI to this repo? #47
• Switching to React:
  • Fixes Playground: Consider simplifying by removing go-angularjs dependency. #64
  • Create a React bindings for GopherJS
  • Adding light and dark mode
  • Updating CSS
  • Adding line numbers to fix Playground: Add line numbers #61
  • Made fancy checkboxes
  • Improved dynamic layout
• Adding predefined snippets
• Adding more programmer interactions:
  • Ctrl+/ will comment the selected lines or current line
  • Tab and Shift+Tab will indent and outdent the selected lines
  • Improved automatic indenting
  • Added bracket and other symbol pairing
  • Added hooks for things like Ctrl+S
  • Improving cursor tracking to address Playground: Minor issue, caret is not kept in view when pressing Enter, Tab. #18
  • Fixed undo/redo stack for Format button breaks undo #54
  • Changed editor to use runes to help editing with unicode
    • May fix Playground: Fails to run some code with Unicode. #68
• Updating the compiler
  • Fixed the precompiler to use new form of sources
  • Changed the compiler to use new parsing configuration
  • Made the compiler run in a web worker
    • May fix Playground: Pull out the core so it can be reused #9
  • Made the compiled JS run in a web worker
    • This allows that long processes to be terminated
    • Keeps the playground responsive while code is running
    • Should address Playground: Add sandboxed iframe #5
  • Made compile errors highlight the line numbers next to the code of the error
• Improving Encapsulation for testability and reusability
• and more...

[nevkontakte]

I'll be honest and admit that I gave a cursory look to most of the code here.

Personally, I feel like React is a bit of an overkill for what Playground is, but it's an iprovement over the status quo, and if nothing else a pretty useful tech demo, so I have no real objection.

Thanks!

[grantnelson-wf]

Personally, I feel like React is a bit of an overkill for what Playground is, but it's an iprovement over the status quo, and if nothing else a pretty useful tech demo, so I have no real objection.

Yeah, React is a little overkill. This totally was totally a tech demo (I wanted it in as much Go as possible) and a learning tool for me to try out things I haven't done much of before, and I probably went overboard since I was having fun. I tinkered on this project on the side for several months while waiting for some CI to finish, between meetings, and even during very slow boring meetings. It has lots of room for improvement and I hope many people add to it.

Note: I can not merge this work since I don't have permissions to gopherjs.github.io like I do for gopherjs, so I'll need your help merging once this is ready.