Test addons on windows test-ci

[Fishrock123]

Looks like window's test-ci doesn't include addons, where makefile does.

Do we have any idea what would be necessary to run these on the windows CI? It seems fairly important.

Related: #2830

cc @nodejs/build

[bnoordhuis]

Also related: #2428.

I'm not sure if batch file scripting is flexible enough to handle building add-ons, in particular ones scraped from the documentation. We'd probably either need to build them unconditionally or implement a poor man's make in JS or python.

For the CI, it's fine to build them from scratch every time. It's kind of annoying when developing locally though.

[mathiask88]

For the sake of completeness: #2537

[Fishrock123]

@mathiask88 Ah good catch :)