TypeScript parsing support

[thescientist13]

Summary

As a stop gap until a proper generic solution can be achieved for #122 , it would be incredibly valuable to support TypeScript (but not necessarily the type checking part) so custom elements can be authored in TypeScript

Details

Ideally would like to support the full range of extensions:

• .js
• .jsx
• .ts
• .tsx (nice to have)

Couple options are:

1. acorn-typescript
2. sucrase
3. typescript (tsc) - less than ideal since we would end up bundling the entire CLI into any SSR use cases, but should work