Cache module interfaces to load them from disk if the source hasn't been touched

[aboeglin]

When we compile a module we have a few steps:

• source ast
• canonical ast
• solved ast
• core ast
• generated object file or js file

The idea would be that during the compilation we would save to disk two things:

• an interface file containing enough information for imports, this info would be a mix of what is currently stored in the canonical ast ( types declarations mostly ) and in the solved ast ( instances, exported top level definitions )
• the target file ( object file or js file )

Then from the cache we could just retrieve everything to satisfy imports and then skip later phases of Core and Codegen as the generated output file would already be up-to-date.