* chore: migrate to Mitt as the EventEmitter
This commit moves us to using Mitt [1] for the event emitter in
Puppeteer. This removes our dependency to Node's EventEmitter which is
part of a larger stream of work to enable a Puppeteer-web version that
doesn't depend on Node.
There are no large breaking changes as we support the main methods that
EventEmitter had, but it also provides some methods that Puppeteer
didn't use. Technically end users could depend on this but it's
unlikely.
[1]: https://github.com/developit/mitt
We should import them just like any other module. This commit makes that
change. It does not change any behaviours or the types themselves.
EXPECTED_PROTOCOL_DIFF as we're updating the structure of it.
* chore: migrate src/Page.js to TypeScript
The final one! This is a huge file and needs to be split up and tidied,
but for now I've left all the definitions in place and converted types
accordingly.
There's some additional tidying we can do now every `src` file is TS,
but I'll leave that for another PR to avoid this one getting any bigger.
Co-authored-by: Mathias Bynens <mathias@qiwi.be>
