Tests: migrate testing infrastructure to minimal dependencies

Tests: migrate testing infrastructure to minimal dependencies

This is a complete rework of our testing infrastructure. The main goal is to modernize and drop deprecated or undermaintained dependencies (specifically, grunt, karma, and testswarm). We've achieved that by limiting our dependency list to ones that are unlikely to drop support any time soon. The new dependency list includes:

- `qunit` (our trusty unit testing library)
- `selenium-webdriver` (for spinning up local browsers)
- `express` (for starting a test server and adding middleware)
  - express middleware includes uses of `body-parser` and `raw-body`
- `yargs` (for constructing a CLI with pretty help text)
- BrowserStack (for running each of our QUnit modules separately in all of our supported browsers)
  - `browserstack-local` (for opening a local tunnel. This is the same package still currently used in the new Browserstack SDK)
  - We are not using any other BrowserStack library. The newest BrowserStack SDK does not fit our needs (and isn't open source). Existing libraries, such as `node-browserstack` or `browserstack-runner`, either do not quite fit our needs, are under-maintained and out-of-date, or are not robust enough to meet all of our requirements. We instead call the [BrowserStack REST API](https://github.com/browserstack/api) directly.

## BrowserStack Runner
- automatically retries individual modules in case of test failure(s)
- automatically attempts to re-establish broken tunnels
- automatically refreshes the page in case a test run has stalled
- runs all browsers concurrently and uses as many sessions as are available under the BrowserStack plan. It will wait for available sessions if there are none.
- supports filtering the available list of browsers by browser name, browser version, device, OS, and OS version (see `npm run test:unit -- --list-browsers` for more info). It will retrieve the latest matching browser available if any of those parameters are not specified.
- cleans up after itself (closes the local tunnel, stops the test server, etc.)
- Requires `BROWSERSTACK_USERNAME` and `BROWSERSTACK_ACCESS_KEY` environment variables.

## Selenium Runner
- supports running any local browser as long as the driver is installed, including support for headless mode in Chrome, FF, and Edge
- supports running `basic` tests on the latest [jsdom](https://github.com/jsdom/jsdom#readme), which can be seen in action in this PR (see `test:browserless`)
- Node tests will run as before in PRs and all non-dependabot branches, but now includes tests on real Safari in a GH actions macos image instead of playwright-webkit.
- can run multiple browsers and multiple modules concurrently

Other notes:
- Stale dependencies have been removed and all remaining dependencies have been upgraded with a few exceptions:
  - `sinon`: stopped supporting IE in version 10. But, `sinon` has been updated to 9.x.
  - `husky`: latest does not support Node 10 and runs on `npm install`. Needed for now until git builds are migrated to GitHub Actions.
  - `rollup`: latest does not support Node 10. Needed for now until git builds are migrated to GitHub Actions.
- BrowserStack tests are set to run on each `main` branch commit
- `debug` mode leaves Selenium browsers open whether they pass or fail and leaves browsers with test failures open on BrowserStack. The latter is to avoid leaving open too many sessions.
- This PR includes a workflow to dispatch BrowserStack runs on-demand
- The Node version used for most workflow tests has been upgraded to 20.x
- updated supportjQuery to 3.7.1

Run `npm run test:unit -- --help` for CLI documentation

Close gh-5418