Dynamic loading of dylibs in proc macro server

[piotmag769]

Currently the proc macro server only starts in a current directory, resolves the workspace and loads needed proc macros from all compilation units (the set of proc macros is fixed after that). The problem is that when we open other a package from other workspace that requires additional proc macros, we won't be able to resolve some macros in that package.

The proposed solution is to add a possibility to send a request to proc macro server that will make the server compile and load the proc macro. The request should contain a path with path to Scarb.toml of the proc macro - we should obtain the path from scarb metadata when we first enter a workspace.