build: Upgrade to TypeScript 4.5 (#151)

This will enable upgrading to Jest 29, which [requires] TypeScript 4.5 if `jest-environment-jsdom` is used.

I did this:

    npm install --save-dev --save-exact [email protected]

Then I got this warning when running `npm run lint`:

    WARNING: You are currently running a version of TypeScript which is not officially supported by @typescript-eslint/typescript-estree.

    You may find that it works just fine, or you may not.

    SUPPORTED TYPESCRIPT VERSIONS: >=3.3.1 <4.5.0

    YOUR TYPESCRIPT VERSION: 4.5.5

    Please only submit bug reports when using the officially supported version.

So I did this:

    npm install --save-dev @typescript-eslint/eslint-plugin@^4

It didn't help, so I did this:

    npm install --save-dev @typescript-eslint/eslint-plugin@^5 @typescript-eslint/parser@^5

## Breaking?

See #145 for details on why this should possibly be considered a breaking change.

I consider it backward compatible, because I don't think any consumer is broken by it. Notably, building with and without this PR in different Git working trees and using `git diff --no-index` to diff the emitted code (`build/` and `lib/`) reveals that it is exactly identical.

[requires]: https://jestjs.io/docs/upgrading-to-jest29#jsdom-upgrade