Adopt @playwright/test and improve integration tests

[Tyriar]

Fixes #3446
Fixes #3326

Changes summary:

• Use playwright test runner instead of plain playwright with mocha
• Move from deprecated equals to strictEquals
• Use JSHandle for most things instead of raw page.evaluate(string) to strongly type renderer-side test code
  • The main thing to be careful with here is not to use async/await inside the page callback as the compiled __awaiter won't be on the page
• Add missing test for onBinary event
• Use () => {} for all tests
• Not using the string for page.evaluate allows us to avoid the \\ hack
• Pretty much all write/term calls now use await and can guarantee the action is complete (eg. writes are parsed) by the time it returns in node, so we can avoid using pollFor for most tests
• Events are now proxied, making it more convenient to test with

Remaining:

• Migrate addon tests over
• Delete old .api tests
• Get all tests passing in CI

[mxschmitt]

nit: In the config you can add: forbidOnly: !!process.env.CI that's how we do it, then you can drop the --forbid-only CLI argument everywhere.

[mxschmitt]

Suggested change

	displayName: 'Install PlayWright browsers'
	displayName: 'Install Playwright browsers'

It's Playwright 🙂

[Tyriar]

@mxschmitt now that you're here, any idea how to solve this? Installing didn't see to fix:

  6) [Firefox Stable] › ../../test/playwright/CharWidth.test.ts:20:5 › CharWidth Integration Tests › getStringCellWidth › ASCII chars 

    browserType.launch: Executable doesn't exist at /home/vsts/.cache/ms-playwright/firefox-1335/firefox/firefox
    ╔═════════════════════════════════════════════════════════════════════════╗
    ║ Looks like Playwright Test or Playwright was just installed or updated. ║
    ║ Please run the following command to download new browsers:              ║
    ║                                                                         ║
    ║     npx playwright install                                              ║
    ║                                                                         ║
    ║ <3 Playwright Team                                                      ║
    ╚═════════════════════════════════════════════════════════════════════════╝

[mxschmitt]

Most likely because you have playwright and @playwright/test inside your package.json with different versions. I suggest to remove playwright and only have @playwright/test with the latest version.

(everything from playwright is also exported from @playwright/test node/package-wise)

[mxschmitt]

Another idea is since you are using yarn, to use yarn run playwright install instead.

[Tyriar]

This is too stale, it's available for reference when we want to try move to @playwright/test in the future.