Auto merge of #16222 - rosefromthedead:unresolved-assoc-item, r=Veykril

add unresolved-assoc-item assist

I tried to copy from private-assoc-item for this

crates/hir/src/diagnostics.rs

@@ -62,6 +62,7 @@ diagnostics![
     UndeclaredLabel,
     UnimplementedBuiltinMacro,
     UnreachableLabel,
+    UnresolvedAssocItem,
     UnresolvedExternCrate,
     UnresolvedField,
     UnresolvedImport,
@@ -218,6 +219,11 @@ pub struct UnresolvedMethodCall {
     pub assoc_func_with_same_name: Option<AssocItemId>,
 }
 
+#[derive(Debug)]
+pub struct UnresolvedAssocItem {
+    pub expr_or_pat: InFile<AstPtr<Either<ast::Expr, Either<ast::Pat, ast::SelfParam>>>>,
+}
+
 #[derive(Debug)]
 pub struct PrivateField {
     pub expr: InFile<AstPtr<ast::Expr>>,