feat(dashboard,admin-vite-plugin): Add support for outlet routes, loader, and handle (#11305)

**What**
- Add support for defining outlet routes using `@`, e.g. `/src/admin/routes/brands/@create/page.tsx`
- Add support for exporting a `loader` from a route file.
- Add support for exporting a `handle` from a route file.

Example usage of a loader and handle:

```tsx
// src/admin/routes/articles/[id]/page.tsx
import { Button, Container, Heading } from "@medusajs/ui";
import {
  Link,
  LoaderFunctionArgs,
  Outlet,
  UIMatch,
  useLoaderData,
} from "react-router-dom";

export async function loader({ params }: LoaderFunctionArgs) {
  const { id } = params;

  return {
    id,
  };
}

export const handle = {
  breadcrumb: (match: UIMatch<{ id: string }>) => {
    const { id } = match.params;
    return `#${id}`;
  },
};

const ProfilePage = () => {
  const { id } = useLoaderData() as Awaited<ReturnType<typeof loader>>;

  return (
    <div>
      <Container className="flex justify-between items-center">
        <Heading>Article {id}</Heading>
        <Button size="small" variant="secondary" asChild>
          <Link to="edit">Edit</Link>
        </Button>
      </Container>
      {/* This will be used for the next example of an Outlet route */}
      <Outlet />
    </div>
  );
};

export default ProfilePage;
```

In the above example we are passing data to the route from a loader, and defining a breadcrumb using the handle.

Example of a outlet route:

```tsx
// src/admin/routes/articles/[id]/@edit/page.tsx
import { Button, Container, Heading } from "@medusajs/ui";

const ProfileEditPage = () => {
  return (
    <div>
      {/* Form goes here */}
    </div>
  );
};

export default ProfileEditPage;
```
This outlet route will be rendered in the <Outlet /> in the above example when the URL is /articles/1/edit

Resolves CMRC-913, CMRC-914, CMRC-915

packages/admin/admin-vite-plugin/src/routes/__tests__/generate-routes.spec.ts

@@ -54,15 +54,112 @@ const expectedRoutesWithoutLoaders = `
     routes: [
         {
             Component: RouteComponent0,
-            path: "/one",
+            path: "/one"
         },
         {
             Component: RouteComponent1,
-            path: "/two",
+            path: "/two"
         }
     ]
 `
 
+const mockFileContentsWithParallel = [
+  // Parent route
+  `
+    import { defineRouteConfig } from "@medusajs/admin-sdk"
+    const Page = () => {
+        return <div>Brands</div>
+    }
+    export const config = defineRouteConfig({
+        label: "Brands",
+    })
+    export default Page
+  `,
+  // Parallel route
+  `
+    import { defineRouteConfig } from "@medusajs/admin-sdk"
+    const Page = () => {
+        return <div>Create Brand</div>
+    }
+    export const config = defineRouteConfig({
+        label: "Create Brand",
+    })
+    export default Page
+  `,
+]
+
+const expectedRoutesWithParallel = `
+    routes: [
+        {
+            Component: RouteComponent0,
+            path: "/brands",
+            children: [
+                {
+                    Component: RouteComponent1,
+                    path: "/brands/create"
+                }
+            ]
+        }
+    ]
+`
+
+const mockFileContentsWithHandleLoader = [
+  `
+    import { defineRouteConfig } from "@medusajs/admin-sdk"
+
+    const Page = () => {
+        return <div>Page 1</div>
+    }
+
+    export const handle = {
+      someConfig: true
+    }
+
+    export const loader = async () => {
+      return { data: true }
+    }
+
+    export const config = defineRouteConfig({
+        label: "Page 1",
+    })
+
+    export default Page
+  `,
+  `
+    import { defineRouteConfig } from "@medusajs/admin-sdk"
+
+    const Page = () => {
+        return <div>Page 2</div>
+    }
+
+    export async function loader() {
+      return { data: true }
+    }
+
+    export const config = defineRouteConfig({
+        label: "Page 2",
+    })
+
+    export default Page
+  `,
+]
+
+const expectedRoutesWithHandleLoader = `
+  routes: [
+    {
+      Component: RouteComponent0,
+      path: "/one",
+      handle: handle0,
+      loader: loader0
+    },
+    {
+      Component: RouteComponent1,
+      path: "/two",
+      loader: loader1
+    }
+  ]
+`
+
 describe("generateRoutes", () => {
   it("should generate routes", async () => {
     const mockFiles = [
@@ -103,4 +200,70 @@ describe("generateRoutes", () => {
       utils.normalizeString(expectedRoutesWithoutLoaders)
     )
   })
+  it("should handle parallel routes", async () => {
+    const mockFiles = [
+      "Users/user/medusa/src/admin/routes/brands/page.tsx",
+      "Users/user/medusa/src/admin/routes/brands/@create/page.tsx",
+    ]
+    vi.mocked(utils.crawl).mockResolvedValue(mockFiles)
+
+    vi.mocked(fs.readFile).mockImplementation(async (file) =>
+      Promise.resolve(
+        mockFileContentsWithParallel[mockFiles.indexOf(file as string)]
+      )
+    )
+
+    vi.mocked(fs.stat).mockRejectedValue(new Error("File not found"))
+
+    const result = await generateRoutes(
+      new Set(["Users/user/medusa/src/admin"])
+    )
+    expect(utils.normalizeString(result.code)).toEqual(
+      utils.normalizeString(expectedRoutesWithParallel)
+    )
+  })
+  it("should handle parallel routes with windows paths", async () => {
+    const mockFiles = [
+      "C:\\medusa\\src\\admin\\routes\\brands\\page.tsx",
+      "C:\\medusa\\src\\admin\\routes\\brands\\@create\\page.tsx",
+    ]
+    vi.mocked(utils.crawl).mockResolvedValue(mockFiles)
+
+    vi.mocked(fs.readFile).mockImplementation(async (file) =>
+      Promise.resolve(
+        mockFileContentsWithParallel[mockFiles.indexOf(file as string)]
+      )
+    )
+
+    vi.mocked(fs.stat).mockRejectedValue(new Error("File not found"))
+
+    const result = await generateRoutes(new Set(["C:\\medusa\\src\\admin"]))
+
+    expect(utils.normalizeString(result.code)).toEqual(
+      utils.normalizeString(expectedRoutesWithParallel)
+    )
+  })
+  it("should handle routes with handle and loader exports", async () => {
+    const mockFiles = [
+      "Users/user/medusa/src/admin/routes/one/page.tsx",
+      "Users/user/medusa/src/admin/routes/two/page.tsx",
+    ]
+    vi.mocked(utils.crawl).mockResolvedValue(mockFiles)
+
+    vi.mocked(fs.readFile).mockImplementation(async (file) =>
+      Promise.resolve(
+        mockFileContentsWithHandleLoader[mockFiles.indexOf(file as string)]
+      )
+    )
+
+    vi.mocked(fs.stat).mockRejectedValue(new Error("File not found"))
+
+    const result = await generateRoutes(
+      new Set(["Users/user/medusa/src/admin"])
+    )
+
+    expect(utils.normalizeString(result.code)).toEqual(
+      utils.normalizeString(expectedRoutesWithHandleLoader)
+    )
+  })
 })