This PR moves the puppeteer source code into separate mono-repo packages:
- `puppeteer` and `puppeteer-core` are now separated into their own
packages.
- `puppeteer-core` has a new exports called `puppeteer-core/internal`
for internal usage.
Tests and various tools have been updated to accommodate the migration.
This PR adds a basic support for WebDriver BiDi that currently includes only the ability to establish a connection and shutdown the browser. Therefore, the implementation is marked as internal and won't show up in the changelog as it's barely useful at the moment.
The API classes are kept as classes instead of interfaces so that clients relying on instanceof checks still work.
