[Workers] Document wrangler's new unstable_dev API (#5739)

* add a page for the API

* Update api.md

* Update api.md

* Update api.md

* Update api.md

* Update api.md

* Update content/workers/wrangler/api.md

Co-authored-by: Pete Bacon Darwin <pete@bacondarwin.com>

* Update api.md

* Add return type, and preamble to usage

* tweaks

* Apply suggestions from code review

Co-authored-by: Kate Tungusova <70746074+deadlypants1973@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Pete Bacon Darwin <pete@bacondarwin.com>

* address feedback

* Update content/workers/wrangler/api.md

Co-authored-by: Pete Bacon Darwin <pete@bacondarwin.com>

* tweak order

* revert

* make ts default

* Revert "make ts default"

This reverts commit 0e196e1d02cb3953437872185416fb0016ca80cc.

* Apply suggestions from code review

* Update content/workers/wrangler/api.md

* Update content/workers/wrangler/api.md

Co-authored-by: Pete Bacon Darwin <pete@bacondarwin.com>
Co-authored-by: Kate Tungusova <70746074+deadlypants1973@users.noreply.github.com>