Enable module level caching using the QueryEngine

[JoshuaBatty]

We should be able to enable this with the current setup. We would basically be caching the below type, allowing us to skip compilation for that module if no changes were detected.

#[derive(Clone, Debug)]
pub struct TyModule {
    pub span: Span,
    pub submodules: Vec<(ModName, TySubmodule)>,
    pub namespace: namespace::Namespace,
    pub all_nodes: Vec<TyAstNode>,
    pub attributes: transform::AttributesMap,
}

There will most likely need to be some changes to the garbage collection so we can remove stale types where changed path == SourceId

This should see a pretty dramatic performance increase in the language server for sway projects with lots of files.