The package that solved my issue was libgirepository1.0-dev. Just noting it down here for the next time I run into the same issue. I bet this naming makes sense somehow for someone, but ... it really doesn't click for me.
(The inconsistency around libgtk-3-0-dbgsym and libgtk-3-dev (and also libgtk2.0-dev) is even worse though.)
@dos Thanks!
I guess I have been using Arch for too long, but these package naming obscurities in Debian (there's a package named gobject-introspection-1.0 after all) really confuse me.