build: enable bundle_dts for core package (#28884)

`ng_module` will now include an `src/r3_symbol.d.ts` when compiling the core package under `ngc` togather with `dts bundling`, This is due that `ngcc` relies on this file to be present, but the `r3_symbols` file which is not part of our public api.

With this change, we can now ship an addition dts file which is flattened.

PR Close #28884

packages/bazel/src/api-extractor/index.ts

@@ -114,5 +114,19 @@ api-extractor: running with
   }
 
   const [tsConfig, entryPoint, dtsBundleOut] = process.argv.slice(2);
-  process.exitCode = runMain(tsConfig, entryPoint, dtsBundleOut);
+  const entryPoints = entryPoint.split(',');
+  const dtsBundleOuts = dtsBundleOut.split(',');
+
+  if (entryPoints.length !== entryPoints.length) {
+    throw new Error(
+        `Entry points count (${entryPoints.length}) does not match Bundle out count (${dtsBundleOuts.length})`);
+  }
+
+  for (let i = 0; i < entryPoints.length; i++) {
+    process.exitCode = runMain(tsConfig, entryPoints[i], dtsBundleOuts[i]);
+
+    if (process.exitCode !== 0) {
+      break;
+    }
+  }
 }