What texture maps are needed to be baked from Blender for setting up a glass material in Unity for it to be called a PBR glass material?
You might bake a roughness map if you need one, but beyond that there aren't really any textures needed - it's all about the shaders and will depend on Unity's implementation or whatever custom Unity shader you create. It could probably be called PBR if the material uses roughness and Fresnel, but when it comes to things that are difficult to render in real time (like glass) the standards are all over the place and you should just go with whatever looks best for your context.