juvix init generated juvix.yaml is incompatible with the internal-build-dir

[paulcadman]

A juvix project created using juvix init comes with a pre-populated dependencies field that points to the stdlib dependency in the default build directory .juvix-build:

juvix.yaml

dependencies:
- .juvix-build/stdlib/
name: foo
version: 0.0.0

However we allow users of juvix compile to override the build directory using the --internal-build-dir flag. This currently works because (see #2273) the default stdlib is always copied to .juvix-build/stdlib, the --internal-build-dir.

To fix this we could implement:

• Put the standard library under a global directory by default #1994

and then have some way of referencing the global project dir in a dependency (perhaps with a magic #GLOBAL_PROJECT variable?, though this is ugly, but the global project location is dynamic, it depends on XDG_CONFIG_HOME).

dependencies:
- #GLOBAL_PROJECT/<current_juvix_version_at_juvix_init_invokcation_time>/stdlib

[paulcadman]

Discussed with the team.

We should use an external dependency for the standard library:

dependencies:
- git:
     url: https://github.com/anoma/juvix-stdlib
     name: stdlib
     ref: v1.2.3  

We should publish releases of the standard library before doing this:

• Publish releases with changelog and version juvix-stdlib#83