ASP.Net and Microsoft NetCore not supported effectively
NetCore is a new microsoft technology, it's opensource and it could be interesting to add in gnome-builder, in settings ASP is in the list of available programming language but in fact .cshtml and some file types are not supported.
Some filetype syntax coloration must be add i think like .cshtml or .vbhtml.
Maybe you see c# like gtk# and gnome app development with c# but it could be cool to integrate netcore development, it's a modern and popular development framework therefore maybe remove .meson files in empty project template.