build: expose locales as package export for ES module resolution (#43431)

As part of v13, all APF packages use the `exports` field which defines
the public entry-points/mappings for a package. so-called package exports.

The `ng_package` rule creates all the necessary mappings/sub-path exports
for the entry-points of `@angular/common`. Though, since the locale files are
generated separately and are not an actual entry-point, we need to expose these
files publicly so that they can be imported/resolved by consumers.

PR Close #43431

packages/bazel/test/ng_package/common_package.spec.ts

@@ -114,6 +114,8 @@ describe('@angular/common ng_package', () => {
             node: './fesm2015/upgrade.mjs',
             default: './fesm2020/upgrade.mjs',
           },
+          './locales/global/*': {default: './locales/global/*.js'},
+          './locales/*': {default: './locales/*.mjs'},
         }
       }));
     });

packages/common/package.json

@@ -11,6 +11,14 @@
   "dependencies": {
     "tslib": "^2.3.0"
   },
+  "exports": {
+    "./locales/global/*": {
+      "default": "./locales/global/*.js"
+    },
+    "./locales/*": {
+      "default": "./locales/*.mjs"
+    }
+  },
   "peerDependencies": {
     "@angular/core": "0.0.0-PLACEHOLDER",
     "rxjs": "^6.5.3 || ^7.0.0"