convert all type declaration files to TS syntax (.d.ts)

[turadg]

What is the Problem Being Solved?

Defining types within JSDoc lacks some features of .ts syntax. For example, documenting properties of objects nested in the type.

It's also understood by less tooling, such as GitHub's web-based code navigator.

Description of the Design

Apply the transformations in #8335 across the codebase. Specifically,

• rename ambient types to types-ambient.js
• use yarn prepack to create the .d.ts files
• empty out the corresponding .js files with a consistent comment explaining why they're empty

Security Considerations

n/a

Scaling Considerations

n/a

Test Plan

CI suffices

Upgrade Considerations

n/a