This is a bit of self promotion, but while trying out writing user defined projections using VS Code, I felt like there is a need for an extension.
So I wrote a snippets extension here: https://marketplace.visualstudio.com/items?itemName=aseemchiplonkar.projections-eventstore
I am working on getting language server in place so that it will support code completion and syntax highlighting (piggybacks JS syntax highlighting as of now) as well.
I hope someone finds this useful 
Cheers,
Aseem