Continue updating infrastructure

[wycats]

Highlights

• Update rollup and associated packages
• Update broccoli and associated packages
• Update other node packages like execa, chalk, etc.
• Update babel usage to use preset-env and rely on TypeScript for the
  initial compilation.
• Update tsconfig to useDefineForClassFields.

Details

We were already relying on TypeScript for first-pass compilation, so the
babel usage was somewhat duplicative and therefore confusing.

The change to useDefineForClassFields revealed a ton of fields
declared as field!: Type, which means field = undefined in standard
JavaScript, and therefore overrides getters, setters or even fields with
initializers defined on any superclass.

This commit changes those fields to declare field: Type. This
transpiles to nothing, leaving any superclass fields alone.

Because the test suite uses Stage 1 decorators, this commit adds back
useDefineForClassFields: false in the build process. This combination
should help to detect any reliance on non-standard behavior during type
checking without breaking the current setup.