Expose HTTPRequest class in public API

[sgrimm]

Release 3.2.0 renamed the Request class to HTTPRequest and the release notes say it's not a breaking change because the class isn't exposed directly.

But it's the documented type of several events: https://github.com/puppeteer/puppeteer/blob/e67a860eb093c46fc33a5d265137f392c767b69d/docs/api.md#class-httprequest

It should be exposed in the public API so application code can use the correct type in event handlers.

[jackfranklin]

We don't yet expose the types for anything on purpose - we're working on shipping types very soon: #6124 . We're also working on new docs (#6118) - a combination of those will help with regards to types.

[stale]

We're marking this issue as unconfirmed because it has not had recent activity and we weren't able to confirm it yet. It will be closed if no further activity occurs within the next 30 days.

[stale]

We are closing this issue. If the issue still persists in the latest version of Puppeteer, please reopen the issue and update the description. We will try our best to accomodate it!