Consider how variable MSBuild Global Properties should be handled by FSAC (specifically the project system)

Wonder if it's worth having a `--msbuild-global-properties` CLI flag for FSAC that you could do like `MSBuildProperty=Foobar,AnotherProperty=false` and pass to proj-info it's not a hardcoded list. More escape hatch kind of stuff if msbuild related stuff changes we don't _have_ to release a fix right away.

_Originally posted by @TheAngryByrd in https://github.com/fsharp/FsAutoComplete/pull/1053#discussion_r1111288996_

My response:
> ohhhhh, I see. That would be a nice addition, but to me it almost speaks to a problem in proj-info instead - we need to be able to change the global properties during runtime and re-trigger evaluation based on that. Classic example is how we hard-code Debug right now. So instead of a CLI flag I think I'd prefer a config setting in Ionide that would map to a JSON-RPC call to set specific global properties for a project, which would flow into proj-info as required. This is a bit bigger of a problem space, though.