4034: Add semantic tag for unresolved references r=matklad a=matklad
This is a quick way to implement unresolved reference diagnostics.
For example, adding to VS Code config
"editor.tokenColorCustomizationsExperimental": {
"unresolvedReference": "#FF0000"
},
will highlight all unresolved refs in red.
Co-authored-by: Aleksey Kladov <aleksey.kladov@gmail.com>