build(bazel): do not build rxjs from source under Bazel (#28720)

PR Close #28720

packages/examples/core/BUILD.bazel

@@ -22,6 +22,7 @@ ng_module(
         "//packages/platform-browser-dynamic",
         "//packages/platform-browser/animations",
         "//packages/router",
+        "@ngdeps//rxjs",
     ],
 )
 
@@ -42,7 +43,10 @@ ts_devserver(
     entry_module = "@angular/examples/core/main",
     index_html = "//packages/examples:index.html",
     port = 4200,
-    scripts = ["@ngdeps//node_modules/tslib:tslib.js"],
+    scripts = [
+        "@ngdeps//node_modules/tslib:tslib.js",
+        "//tools/rxjs:rxjs_umd_modules",
+    ],
     static_files = [
         "@ngdeps//node_modules/zone.js:dist/zone.js",
         "@ngdeps//node_modules/zone.js:dist/task-tracking.js",