In older versions of Ubuntu (up to 17.10), there was the package
geany-plugin-debugger. Is there a special reason why there is no such package in Ubuntu 18.04? For all other
geany plugins, there seem to be corresponding packages
The reason seems to be that webkitgtk-3.0 is deprecated. From changelog:
"Disable webkit-using plugins: markdown, webhelper webkitgtk-3.0 is not to be used as it is deprecated, but the port to webkit2gtk-4.0 isn't ready yet."