Explore type level integration without bonding to compiler

[matprec]

Binding ourself to the compiler will remove make us cumbersome. Instead, provide a TypeQuery trait, wich the caller will implement. This makes it possible, to e.g. leverage the RLS capabilities without fixing ourself to the compiler, as the would update the query trait on its own.

Specific design is open. Some thoughts:

is_type_from_std(&ast::TyKind) / query_type_id(&ast::TyKind). The caller would need to be able to provide more information, especially in generic contexts, where the type of a function is defined by inference.

Goals

• coercions (deref, but not only) – where they happen, why they happen
• desugaring of operators
• Annotate fat pointers (trait objects)