Add config to unconditionally prefer core imports over std

Fixes https://github.com/rust-lang/rust-analyzer/issues/12979

crates/ide-diagnostics/src/handlers/missing_fields.rs

@@ -124,6 +124,7 @@ fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::MissingFields) -> Option<Vec<Ass
                         let type_path = current_module?.find_use_path(
                             ctx.sema.db,
                             item_for_path_search(ctx.sema.db, item_in_ns)?,
+                            ctx.config.prefer_core,
                         )?;
 
                         use_trivial_constructor(