feat(admin-bundler,admin-vite-plugin,medusa): Add support for loading Admin Extensions from plugins (#10869)

Should not be merged before https://github.com/medusajs/medusa/pull/10895

**What**
- Introduces a new `plugin` command to `admin-bundler`, currently not used anywhere but will be called from `medusa build:plugin`
- Discovers plugins with extensions and add passes the to `admin-vite-plugin`.
- Updates `admin-vite-plugin` so its able to read built admin extensions.

Resolves CMRC-830, CMRC-839

packages/admin/admin-bundler/src/lib/config.ts

@@ -2,7 +2,6 @@ import { VIRTUAL_MODULES } from "@medusajs/admin-shared"
 import path from "path"
 import { Config } from "tailwindcss"
 import type { InlineConfig } from "vite"
-
 import { BundlerOptions } from "../types"
 
 export async function getViteConfig(

packages/admin/admin-bundler/src/lib/plugin.ts

@@ -0,0 +1,57 @@
+import { readFileSync } from "fs"
+import { glob } from "glob"
+import path from "path"
+import { UserConfig } from "vite"
+
+export async function plugin() {
+  const vite = await import("vite")
+  const entries = await glob("src/admin/**/*.{ts,tsx,js,jsx}")
+
+  const entryPoints = entries.reduce((acc, entry) => {
+    // Convert src/admin/routes/brands/page.tsx -> admin/routes/brands/page
+    const outPath = entry
+      .replace(/^src\//, "")
+      .replace(/\.(ts|tsx|js|jsx)$/, "")
+
+    acc[outPath] = path.resolve(process.cwd(), entry)
+    return acc
+  }, {} as Record<string, string>)
+
+  const pkg = JSON.parse(
+    readFileSync(path.resolve(process.cwd(), "package.json"), "utf-8")
+  )
+  const external = new Set([
+    ...Object.keys(pkg.dependencies || {}),
+    ...Object.keys(pkg.peerDependencies || {}),
+    "react",
+    "react-dom",
+    "react/jsx-runtime",
+    "react-router-dom",
+    "@medusajs/admin-sdk",
+  ])
+
+  const pluginConfig: UserConfig = {
+    build: {
+      lib: {
+        entry: entryPoints,
+        formats: ["es"],
+      },
+      minify: false,
+      outDir: path.resolve(process.cwd(), "dist"),
+      rollupOptions: {
+        external: [...external],
+        output: {
+          globals: {
+            react: "React",
+            "react-dom": "React-dom",
+            "react/jsx-runtime": "react/jsx-runtime",
+          },
+          preserveModules: true,
+          entryFileNames: `[name].js`,
+        },
+      },
+    },
+  }
+
+  await vite.build(pluginConfig)
+}