Fix cyclic dependencies core <-> frontend

[cknitt]

This resolves some cyclic dependencies between jscomp/core and jscomp/frontend, thereby also fixing editor integration for the files in jscomp/frontend.

• frontend can now be compiled as a separate lib instead of copying the frontend .ml(i) files to the core directory.
• The dependency is now unidirectional (core depends on frontend)

To achieve this, I did the following:

• Move js_raw_info.ml and lam_constant.ml(i) from core to frontend
• Adapt a few type definitions

This was the quickest and least invasive way I found to resolve the issue. If any further restructuring is wanted, it can be done in future PRs.

Fixes #5877.

[cristianoc]

Sweet! No more coding without editor support there.
Should formatting also be turned back on.

[cknitt]

We can do a separate PR for formatting.

[mununki]

Thanks! 👍