Improve workflow in monorepos

[jacobp100]

When working in a monorepo (like this - https://github.com/jacobp100/technicalc-core), the build will only start when you open a file in one of the packages, and will only build that package. It would be nice to be able to build all packages concurrently

Also, if you close all open files, the build stops, and needs to be restarted when opening another file

[fhammerschmidt]

I think this will be easier to support in ReScript 11: rescript-lang/rescript#5722

But I am not sure if that assumption is correct. @cristianoc

Related issue: #437

[jacobp100]

I think that PR looks useful - but won't change things in the monorepo I linked: (by chance) every package that uses a pinned dependency includes all the child pinned dependencies too. But working across the multiple projects is still difficult, and I still end up invoking the manual build commands in the terminal

I would expect as soon as I open the repo in VSCode - even with no files open - it starts a build of all packages