Expose screenshotting capabilities to the web page content extractor script

[azasypkin]

Summary

Web page content tracker utility should expose screenshotting capabilities to the web page content extractor script. The function should be available through the context argument.

See https://playwright.dev/docs/screenshots#full-page-screenshots and https://chromedevtools.github.io/devtools-protocol/tot/Page/#method-captureScreenshot