Extend expect 28 types directly

[IanVS]

This copies the type definitions from definitely-typed into the repo and augments the expect module with the custom matchers using the non-global approach possible in expect 28+.

Similar to testing-library#483.

[IanVS]

@yannbf, from my local testing this seems like it will work. Here's what I did:

• Checkout this branch, and build it (yarn build).
• In your own project, find @testing-library/jest-dom in node_modules, copy over the new dist, package.json, and index.d.ts.
• Find and remove node_modules/@types/testing-library__jest-dom, just to be safe.
• Also in your project, use the canary version of "@storybook/expect": "28.1.4-canary.0" (may need to use yarn resolutions or npm overrides).

Then, you should still get autocompletion of the custom matchers.

[yannbf]

Hey @IanVS what do you think we need to do with this PR? I remember having discussions with the testing-lib team and apparently they're moving jest-dom into dom-assertions which will allow them to properly upgrade to TS, but I'm not sure if we need to wait?

[IanVS]

I think this isn't necessary if we go with storybookjs/expect#12. As far as I can tell, no progress is being made in jest-dom nor dom-assertions.