Closes https://github.com/microsoft/playwright/issues/32159. I
originally set out to enable Strict Mode for our React UI, but found a
way better thing: Enabling the lint rules we had already installed!
`eslint-plugin-react` is already in of our `package.json`, and this PR
enables it and fixes some of the reported issues. Most of them are
around the `key` prop which is mostly about performance, but there's
also fixes for misspelled `data-testid` props.
This lets our spec files be .ts instead of just .js. The typescript files will be checked against the public types. Tests are compiled with babel just in time before running them, emulating the jest experience. TypeScript tests are also linted with eslint.
I converted keyboard.spec.js as the first demo. I'll follow up converting some more more tests.
