Add vscode extension

[jabraham17]

This PR replaces everything in this repo with a vscode extension written in TypeScript that contributes a number of features

Features

• Syntax highlighting for the Chapel language
  • This was rewritten from scratch based on https://github.com/chapel-lang/chapel-tmbundle
  • Rewritten in JSON to be easier to read and maintain
  • Separated regexs in logical blocks improve readability
  • Fixed bugs with comments and strings
  • Support for extern blocks
  • Easier to extend than the old tmBundle
• A client for the chplcheck LSP server
  • If a user sets CHPL_HOME in the vscode config and has the python bindings built, can find and run chplcheck in LSP mode
• A client for the chpl-language-server
  • If a user sets CHPL_HOME in the vscode config and has the python bindings built, can find and run chpl-language-server
• Chapel code snippets
  • supports several parallel loop patterns, as well as a basic hello world
• An icon for .chpl files
• Syntax highlighting for the Chapel AST, dumped by the compiler

[Reviewed by @ShreyasKhandekar]

[jabraham17]

I was looking for a way to see what subset of features of the LSP this extension supports, maybe a checklist of sorts? Is there a way for us to see that?

I have rewritten the README with this information