This PR updates the troubleshooting guide with some information
regarding the new `exports` resolution and cache directory.
This PR also reformats some of the other MD documents.
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.
