feat: support mts, cts, mjs and cts files in source code (#595)

### Summary

currently these files get treated as assets and are copied over as is.
however this is not the correct behavior. this changes them to be trated
as source code.

in addition, the module syntax in .mts or .mjs files is preserved as is.

### Test plan

tested in a generated project by creating `.mts` and `.cts` files.

Author: satya164

packages/react-native-builder-bob/src/utils/compile.ts

@@ -15,6 +15,8 @@ type Options = Input & {
   exclude: string;
 };
 
+const sourceExt = /\.([cm])?[jt]sx?$/;
+
 export default async function compile({
   root,
   source,
@@ -73,17 +75,15 @@ export default async function compile({
     });
   }
 
-  const outputExtension = '.js';
-
   await Promise.all(
     files.map(async (filepath) => {
       const outputFilename = path
         .join(output, path.relative(source, filepath))
-        .replace(/\.(jsx?|tsx?)$/, outputExtension);
+        .replace(sourceExt, '.$1js');
 
       await fs.mkdirp(path.dirname(outputFilename));
 
-      if (!/\.(jsx?|tsx?)$/.test(filepath)) {
+      if (!sourceExt.test(filepath)) {
         // Copy files which aren't source code
         fs.copy(filepath, outputFilename);
         return;
@@ -102,7 +102,15 @@ export default async function compile({
           ? null
           : {
               presets: [
-                [require.resolve('../../babel-preset'), { modules, esm }],
+                [
+                  require.resolve('../../babel-preset'),
+                  {
+                    modules:
+                      // If a file is explicitly marked as ESM, then preserve the syntax
+                      /\.m[jt]s$/.test(filepath) ? 'preserve' : modules,
+                    esm,
+                  },
+                ],
               ],
             }),
       });
@@ -136,18 +144,20 @@ export default async function compile({
 
   const getGeneratedEntryPath = async () => {
     if (pkg.source) {
-      const indexName =
-        path.basename(pkg.source).replace(/\.(jsx?|tsx?)$/, '') +
-        outputExtension;
-
-      const potentialPath = path.join(
-        output,
-        path.dirname(path.relative(source, path.join(root, pkg.source))),
-        indexName
-      );
-
-      if (await fs.pathExists(potentialPath)) {
-        return path.relative(root, potentialPath);
+      for (const ext of ['.js', '.cjs', '.mjs']) {
+        const indexName =
+          // The source field may not have an extension, so we add it instead of replacing directly
+          path.basename(pkg.source).replace(sourceExt, '') + ext;
+
+        const potentialPath = path.join(
+          output,
+          path.dirname(path.relative(source, path.join(root, pkg.source))),
+          indexName
+        );
+
+        if (await fs.pathExists(potentialPath)) {
+          return path.relative(root, potentialPath);
+        }
       }
     }