export "#region" support in index file (#320)

add the export in index file which is missed in the PR supporting Region

Author: RodgeFu

.chronus/changes/export-region-support-2025-9-14-11-12-19.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@alloy-js/csharp"
+---
+
+export "#region" support

packages/csharp/src/components/index.ts

@@ -23,6 +23,7 @@ export * from "./parameters/parameters.jsx";
 export * from "./property/property.jsx";
 export * from "./record/declaration.js";
 export * from "./Reference.js";
+export * from "./region/region.jsx";
 export * from "./source-file/source-file.jsx";
 export * from "./struct/declaration.jsx";
 export type { TypeParameterProps } from "./type-parameters/type-parameter.jsx";