Refactoring into TypeScript, cleaning up, and adding significant code documentation

[jake-figma]

Refactoring the codebase to use TypeScript.

Now uses npm and has only two dependencies: typescript, esbuild.

• npm run build to compile code.js
• npm run dev to watch files and build on file change

The UI code is not compiled. It is still raw JS inline inside of HTML files.

Prioritizing simplicity here so that it is easily clone-able and extensible.

Plugin code split between a few files in src:

• code.ts the main plugin code file that is compiled into code.js
• params.ts methods for generating params from a node to fill snippet templates with
• snippets.ts methods for surfacing and hydrating snippet templates with data
• bulk.ts methods for performing bulk operations when run in design mode
• pluginData.ts methods and keys for reading and writing from shared plugin data