Enable cypress for v8

[ecraig12345]

Cypress provides the ability to run tests in a real browser, which is especially useful for certain interactive scenarios such as anything involving focus.

We already have cypress enabled for v9 and v0 but also want to enable it for v8 as well, mainly for components like FocusZone and FocusTrapZone.

v8 tests will be selectively ported to cypress as it makes sense, likely as part of enzyme removal (#21663).