Automatically create a default language when Language is installed by a recipe

This is part of #3591433 (closed). Rather than implement a config action to create the default language, I think it should happen automatically when a recipe installs Language.

This could be ported directly into core; all Language would need to do is add a RecipeAppliedEvent subscriber doing exactly what we're doing in this shim. IMHO, the only blocker to this is creating a core issue that moves the polyfill there.