Debug mode for test runner

[pavelfeldman]

Feature request

Requested on Twitter: https://mobile.twitter.com/eliostruyf/status/1413392602418790401

The ideal would be a test runner
that shows the test progress, and
a separate browser instance.

• My understanding is that this is a new mode

npx playwright test --debug

Which is a shortcut to

PWDEBUG=1 npx playwright test --workers=1 --headed

But in addition to that,

• inspector and browser window are reused to reduce flashing
• elements of the new test status UI show the history of successful/failed runs in the inspector

This basically produces debug experience visually resembling Cypress for those relying only on core testing scenarios.

[mxschmitt]

This got partially implemented in #8938