Improve ref typings for IntrinsicElements.

[loucyx]

This change adds the corresponding constructor type for all IntrinsicElements in JSX, improving ref types, for example the anchor tag now has the HTMLAnchorElement type in it's ref.

This was created with a simple JS script that extracts the constructor.name of every element in the

Object.keys(/* Object with HTMLIntrinsicElements */)
  .map(tag => document.createElement(tag))
  .map(
    ({ constructor, tagName }) =>
      `${tagName.toLowerCase()}: HTMLAttributes<${constructor.name}>;`
  )
  .join("\n");

After running tests I spotted an issue with the preact.tsx test in the ts directory that wasn't detected previously due to the lack of typing in IntrinsicElements. A ref can be an Element or null, but that wasn't being considered in the types of the test.

This is my first PR in here, I hope I'm not messing anything up 😄

[coveralls]

Coverage increased (+0.1%) to 99.891% when pulling c9f5dcb on lukeshiru:better-jsx-refs into 87b945b on preactjs:master.

[loucyx]

Ugh, I used prettier accidentally on preact.tsx, rolling that back X_X

[marvinhagemeister]

@lukeshiru Woa, that's super awesome!! We just merged prettier into master this morning, so you're good to go to use it for formatting 👍 Can you rebase against that and run prettier on your changes? Apart from that it's ready to be merged 🎉 Again, thank you so much for the PR 💯

[loucyx]

@marvinhagemeister I did a rebase on my side and applied the prettier formatting. Let me know if anything else is missing and I'll update accordingly 😄

[marvinhagemeister]

Sweet! This is so good 😍 Thank you so much for your PR 🎉 💯