feat(testing): add .skip alias to bdd test API

[marvinhagemeister]

This PR adds .skip() as an alias of .ignore(). That alias is much more common than .ignore() in popular bdd-style testing APIs in other test runners.

Test runner	Skipping APIs
mocha	describe.skip(), it.skip()
jasmine	xdescribe(), xit()
jest	describe.skip(), it.skip() or xdescribe(), xit()
vitest	describe.skip(), it.skip()

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[kt3k]

Adding .skip makes sense to me (.ignore looks exceptional on that design)

I don't think we should add xit or xdescribe. They are useful only when these keywords are all global variables (you can quickly switch between it <-> xit in that case). If those are exported via ES modules, you need to add import { xit } from ... before switching to xit (and also delete that import when you stop using it). So they are cumbersome to use and have little value in my view.

[marvinhagemeister]

Fair point! I've updated the PR to only add .skip().

[kt3k]

LGTM