How to make a custom asset's source file show up in the generated C# project?

I’m making a custom asset that is very comparable to a shader file, with its own custom extension.

Unity implicitly knows to add files of type .hlsl, .cginc, .shader, and .compute to the .csproj file it generates so that they will be editable in Visual Studio.

Can I get Unity to treat my own custom file type in the same way?