Function implemented_method 

fn implemented_method<'tcx>(
    tcx: TyCtxt<'tcx>,
    instance: Instance<'tcx>,
) -> Option<(EarlyBinder<'tcx, TraitRef<'tcx>>, DefId, DefId)>

Determines if an instance represents a trait method implementation and returns the necessary information for type erasure.

This function handles two main cases:

• Implementation in an impl block: When the instance represents a concrete implementation of a trait method in an impl block, it extracts the trait reference, method ID, and trait ID from the implementation. The method ID is obtained from the trait_item_def_id field of the associated item, which points to the original trait method definition.

• Provided method in a trait block or synthetic shim: When the instance represents a default implementation provided in the trait definition itself or a synthetic shim, it uses the instance’s own def_id as the method ID and determines the trait ID from the associated item.