Expose CPU related metrics from page.metrics() as phantomas metrics

[gmetais]

This pull request adds 6 new metrics, taken from Puppeteer's page.metrics() values:

• layoutCount: total number of full or partial page layout
• layoutDuration: combined durations of all page layouts
• recalcStyleCount: total number of page style recalculations
• recalcStyleDuration: combined duration of all page style recalculations
• scriptDuration: combined duration of JavaScript execution
• taskDuration: combined duration of all tasks performed by the browser

The scriptDuration looks particularly important to me, as pages tend to have more and more JS on the web. More information here: https://github.com/puppeteer/puppeteer/blob/main/docs/api.md#pagemetrics

Don't hesitate if you'd like me to change things such as metrics names, or if I forgot something.

(I can't add tests, as time-based values fluctuate too much. Count values are more stable, but they might also change with browser updates.)

[macbre]

@gmetais - thanks for yet another PR 🙂

[macbre]

I hope that one day we'd be able to use benefits of TypeScript here 🙂

#830