use a different value for Separator and make API check more strict

src/vs/workbench/api/common/extHost.api.impl.ts

@@ -599,7 +599,7 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			},
 			showQuickPick(items: any, options?: vscode.QuickPickOptions, token?: vscode.CancellationToken): any {
 				// TODO: remove this once quickPickSeparators has been finalized.
-				if (Array.isArray(items) && items.some((item) => item.kind !== undefined)) {
+				if (Array.isArray(items) && items.some((item) => item.kind === extHostTypes.QuickPickItemKind.Separator)) {
 					checkProposedApiEnabled(extension, 'quickPickSeparators');
 				}
 				return extHostQuickOpen.showQuickPick(items, options, token);

src/vs/workbench/api/common/extHostTypes.ts

@@ -2929,8 +2929,8 @@ export class QuickInputButtons {
 }
 
 export enum QuickPickItemKind {
+	Separator = -1,
 	Default = 1,
-	Separator = 2,
 }
 
 export enum ExtensionKind {