Why:
* To implement robust cross-project go-to-definition in LSP
i.e you can jump to definition of any global name coming
from library dependencies, as well as from the local project files.
What it does:
* Modify `FC`s to carry `ModuleIdent` for .idr sources,
file name for .ipkg sources or nothing for interactive runs.
* Add `--install-with-src` to install the source code alongside
the ttc binaries. The source is installed into the same directory
as the corresponding ttc file. Installed sources are made read-only.
* As we install the sources pinned to the related ttc files we gain
the versioning of sources for free.
This gives us the ability to define and use implementations locally, in
where clauses/local let bindings, as well as flag local definitions as
hints.
It's not yet quite equivalent to global hints, however, since it translated
the hint to a local let binding, which doesn't reduce, so if something
relies on the reduction behaviour of the hint, it won't work. This
refinement is coming later
