This adds changes to support loading project dependencies in non-file based projects.
The design for this feature can be found in SPICE-0005: https://github.com/apple/pkl-evolution/pull/6
Changes:
* Consider all imports prefixed with `@` as dependency notation.
* Bugfix: fix resolution of glob expressions in a local dependency.
* Adjust pkl.Project:
- Allow local dependencies from a scheme-local paths.
- Disallow certain evaluator settings if not loaded as a file-based module.
* Breaking API change: `ProjectDependenciesManager` constructor now requires `ModuleResolver` and `SecurityManager`.