The `Puppeteer` class had two concerns:
* connect to an existing browser
* launch a new browser
The first of those concerns is needed in all environments, but the
second is only needed in Node.
https://github.com/puppeteer/puppeteer/pull/6484 landing enabled us to
pull the `Puppeteer` class apart into two:
1. `Puppeteer` which hosts the behaviour for connecting to existing
browsers.
2. `PuppeteerNode`, which extends `Puppeteer` and also adds the ability
to launch a new browser.
This is a non-breaking change, because Node users will still get an
instance of a class with all the methods they expect, but it'll be a
`PuppeteerNode` rather than `Puppeteer`. I don't expect this to cause
people any issues.
We also now have new files that are effectively the entry points for
Puppeteer:
* `node.ts`: the main entry point for Puppeteer on Node.
* `web.ts`: the main entry point for Puppeteer on the web.
* `node-puppeteer-core.ts`: for those using puppeteer-core (which only
exists in Node, not on the web).
* chore(agnostify): Create Node and Web initializer.
This PR splits `initialize.ts` into two files, one for web, and one for
Node. The Node initializer requires much more information as it needs to
know which browser(s) to download and where to store them, whereas the
web one does not.
A future PR that I'm working on will tidy up `src/common/Puppeteer.ts`
(as it contains a lot of Node specific logic around downloading and
installing browsers), but this change enables us to stop the browser
bundle attempting to use the `pkg-dir` dependency, which wouldn't work
within a browser, as well as keeping the size of the PRs down and
avoiding one mammoth PR.
