This PR separates the installations tests from normal tests and changes
the matrices as follows:
- Installations tests on all platforms and the latest 3 node versions.
- Chrome tests are done on all platforms on the latest node version.
- Firefox tests are done only on linux on the latest node version.
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.