The vapi files should be provided and maintained by the Geany project
There is no "should" in a totally volunteer project, if someone wants to contribute something they will, otherwise that thing won't exist in teh project.
IIUC the Geany build scripts can build the GIR from the Geany API. [This](https://github.com/kugel-/peasy) project provides it for Python to access Geany and (presumably by vapigen) a vapi all mechanically, not hand built.