Matthew Carlson has written a Visual Studio Code plugin for Microsoft’s Project Mu.
Matthew: if you’re reading this, please consider also supporting Tianocore/EDK2, not just Project Mu, as there is no Tianocore extension for VSCode, so your project would be useful to another community as well.
For other open source IDE support for UEFI, there’s an Eclipse plugin and Visual Studio-based VisualUEFI. For closed-source IDE support, there is Intel ISS and ARM DS-5. Maybe others, I’m not aware of, if you know of one, please leave a Comment.