docs(svelte-testing-library): update API docs for v5 release

[mcous]

This is a documentation companion to testing-library/svelte-testing-library#325. We're introducing a few minor, though technically breaking, changes to the API in the upcoming v5 release (which should be triggered upon merge of the PR above).

This PR updates the API section of the svelte-testing-library docs accordingly, with callouts for users of the current v4.

CC @yanick

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[mcous]

@timdeschryver (pinging you because you’ve reviewed my previous STL docs PRs) we just released v5 to our latest tag, so these docs are ready to go. I’ve synced up and undrafted the PR accordingly

CC @yanick

[mcous]

Thanks for the careful review!

[mcous]

@timdeschryver Is there anything blocking merge here? We just got an inbound issue due to improper API usage that this doc update details

[timdeschryver]

@timdeschryver Is there anything blocking merge here? We just got an inbound issue due to improper API usage that this doc update details

Oops 😅 it got off my radar. Thanks for the ping!