fix: symlink .impl.d files for virtual library modules too

[anmonteiro]

• when setting up rules for implementation files in a virtual library, their artifacts are symlinked to the object directory for the concrete implementation too
• this change adds rules to symlink the ocamldep resulting files too, as they may be needed in the object directory
• specifically, this fixes the failing test in fix(melange): track immediate .cmj deps as dependencies of JS rules #10286 as will be demonstrated once I cherry-pick this commit in that PR.

[rgrinberg]

You say that they may be needed, but more concretely this is needed for melange only? I don't think this is needed anywhere else because I just merge the dependency graphs for vlibs and impls everywhere else and use that.

[anmonteiro]

@rgrinberg thanks. I made it conditional on melange.

[rgrinberg]

Okay, then I'd just include this as a commit in #10286. If it doesn't fix anything on its own, a separate PR isn't really needed.

[anmonteiro]

Sounds good, will incorporate it there.