add region support in csharp (#319)

Co-authored-by: Brian Terlson <brian.terlson@microsoft.com>
Co-authored-by: Timothee Guerin <timothee.guerin@outlook.com>

Author: 3 people

.chronus/changes/csharp-region-2025-9-13-16-38-9.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@alloy-js/csharp"
+---
+
+Add `#region` support

packages/csharp/src/components/region/region.test.tsx

@@ -0,0 +1,19 @@
+import { Children } from "@alloy-js/core/jsx-runtime";
+import { expect, it } from "vitest";
+import { TestNamespace } from "../../../test/utils.jsx";
+import { Region } from "./region.jsx";
+
+const Wrapper = (props: { name: string; children: Children }) => (
+  <TestNamespace>
+    <Region name={props.name}>{props.children}</Region>
+  </TestNamespace>
+);
+
+it("region test", () => {
+  expect(<Wrapper name="Test Region">// This is inside region</Wrapper>)
+    .toRenderTo(`
+      #region Test Region
+      // This is inside region
+      #endregion
+    `);
+});

packages/csharp/src/components/region/region.tsx

@@ -0,0 +1,16 @@
+import { Children, code, List } from "@alloy-js/core";
+
+export interface RegionProps {
+  name: string;
+  children: Children;
+}
+
+export function Region(props: RegionProps) {
+  return (
+    <List>
+      {code`#region ${props.name}`}
+      {props.children}
+      {code`#endregion`}
+    </List>
+  );
+}