Right now, module definitions for modules using the new code splitting feature with codexComponents look like this:

{
    "class": "MediaWiki\\ResourceLoader\\CodexModule",
    "codexComponents": [
        ...
    ],
    "dependencies": [
          "vue"
    ]

If you don't specify vue as a dependency, things break. It makes some amount of sense that you would need to do this, because the code in such a module probably does depend on Vue. But on the other hand, the code pulled in by codexComponents won't work without Vue, so it makes sense for Vue to be an implicit dependency (just as it would be if you listed @wikimedia/codex as a dependency).

We should change CodexModule so that it automatically adds Vue as a dependency when codexComponents is used.