chore(web): re-establish BrowserStack testing for legacy browser support

[jahorton]

Note that at this stage, we have not yet established BrowserStack configs as per #11404 (comment) for nightly testing.

Extracted from #11300. Our use of the new @web/test-runner engine for automated Browser testing currently utilizes playwright, which exclusively tests against current browsers. As discussed in other channels, the long-term plan is to establish nightly tests on BrowserStack to act as 'canary testing' against issues with legacy browser support. (This way, they only run once a day, preventing our generally more-frequent PR test builds from being subjected to the flakiness we've occasionally seen when utilizing BrowserStack.)

[jahorton]

A possible alternative strategy:

It is relatively easy to download older versions of Chromium and test on those -- which I think would be sufficient. That then resolves the need to drag in 5,000 new lines of dependencies into package-lock.json and probably removes most of our BrowserStack requirement altogether?

by @mcdurdin in #11845 (comment)

Especially if we can find a similar route for WebKit, we may be better off doing a round or two of manual testing against these older versions every once in a while.

[mcdurdin]

Especially if we can find a similar route for WebKit, we may be better off doing a round or two of manual testing against these older versions every once in a while.

TBH I am less concerned about WebKit. We have older devices we can test with for Safari and the user base for old devices on those platforms is much smaller.