feat: add deferred executor, support chaining

[kettanaito]

BREAKING CHANGE: Deferred promises are now implemented via the deferred executor function. There are no changes to the existing public API.

Changes

• Supports Promise chaining.
• Adds createDeferredExecutor to use this library with any Promise.
• Improves type annotations in regard to what the deferred promise expects as the input and what is the promise's output:

const p = new DeferredPromise<number>()
  .then(() => 'hello')

// The input must be "number".
p.resolve(5)

// the output is "string"
// (the result of the "then" chain)
await p // "hello"

• Deprecated: Removes DeferredPromise.result. Access the result by awaiting the promise instead.
• Deprecated: The resolved promise state is replaced by fulfilled, which is the correct promise state representation per specification.

Roadmap

• Document the deferred executor with more detail and then mention it in the deferred promise class documentation. That's exactly their relationship.
• Support promises returned from .then/.catch.

[kettanaito]

Released: v2.0.0 🎉

This has been released in v2.0.0!

• 📄 Release notes
• 📦 npm package

Make sure to always update to the latest version (npm i @open-draft/deferred-promise@latest) to get the newest features and bug fixes.

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