Cache the model loaded for the language module and JDK

[FroMage]

We should try to share those modules across every open project, but also try to dump a serialised version of them to disk, to be quickly reloaded. @FroMage has a prototype implementation of that for the JVM backend from a while back. It needs to be rebased, tried, timed and tested. In the past it was not entirely clear that it provided a huge speed gain, but this was only tested with the language module, perhaps the JDK would be a better candidate.