chore: roll to the release-1.8 branch tip

chore(stderr): fix handling without stderr fileno (microsoft#402)

chore: bump cli version to 0.171.0 (microsoft#392)

chore: roll Playwright to 1.7

fix(video): fix the new recordVideo API (microsoft#336)

chore: update readme upon api update (microsoft#308)

chore: roll to Playwright 1.6.2

api: use bytes, not string|bytes for file input buffers (microsoft#254)

tests: mark test as flaky (microsoft#248)

api(video): support video accessor from 1.5.1 (microsoft#238)