fix(dev): build js modules for ts->js conversion

The TS->JS migration was removed from the CLI codemod options, but still
used for TS->JS conversion when creating a new Remix project from the
CLI. The TS modules responsible for the TS->JS conversion were
incorrectly removed from the Rollup build, resulting in the
corresponding built JS modules being absent. That caused the CLI to
error when trying to perform TS->JS conversion. This changes
reintroduces the wiring to build the modules responsible for the TS->JS
conversion.

Fixes #4854

packages/remix-dev/cli/migrate/migrations/transforms.ts

@@ -0,0 +1,2 @@
+// escape-hatch to include these files in the build
+export * as ConvertToJavaScriptTransform from "./convert-to-javascript/transform";

packages/remix-dev/rollup.config.js

@@ -71,6 +71,26 @@ module.exports = function rollup() {
       ],
     },
     getCliConfig({ packageName, version }),
+    {
+      external: (id) => isBareModuleId(id),
+      input: [`${sourceDir}/cli/migrate/migrations/transforms.ts`],
+      output: {
+        banner: createBanner("@remix-run/dev", version),
+        dir: `${outputDist}/cli/migrate/migrations`,
+        exports: "named",
+        format: "cjs",
+        preserveModules: true,
+      },
+      plugins: [
+        babel({
+          babelHelpers: "bundled",
+          exclude: /node_modules/,
+          extensions: [".ts"],
+        }),
+        nodeResolve({ extensions: [".ts"] }),
+        copyToPlaygrounds(),
+      ],
+    },
     {
       external() {
         return true;