refactor(common): move the low level locale registering to core (#33523)

To limit the exposure of the private `LOCALE_DATA` from outside
`@angular/core` this commit exposes private functions in the core
to hide the internal structures better.

* The `registerLocaleData()` implementation has moved from
`@angular/common` to `@angular/core`. A stub that delegates to
core has been left in common for backward compatibility.
* A new `ɵunregisterLocaleData()` function has been provided,
which is particularly useful in tests to clear out registered locales
to prevent subsequent tests from being affected.
* A private export of `ɵregisterLocaleData()` has been removed
from `@angular/common`. This was not being used and is accessible
via `@angular/core` anyway.

PR Close #33523

packages/core/test/i18n/locale_data_api_spec.ts

@@ -0,0 +1,60 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {findLocaleData, registerLocaleData, unregisterLocaleData} from '../../src/i18n/locale_data_api';
+
+{
+  describe('locale data api', () => {
+    const localeCaESVALENCIA: any[] = ['ca-ES-VALENCIA'];
+    const localeEn: any[] = ['en'];
+    const localeFr: any[] = ['fr'];
+    const localeFrCA: any[] = ['fr-CA'];
+    const localeZh: any[] = ['zh'];
+    const localeEnAU: any[] = ['en-AU'];
+
+    beforeAll(() => {
+      registerLocaleData(localeCaESVALENCIA);
+      registerLocaleData(localeEn);
+      registerLocaleData(localeFr);
+      registerLocaleData(localeFrCA);
+      registerLocaleData(localeFr, 'fake-id');
+      registerLocaleData(localeFrCA, 'fake_Id2');
+      registerLocaleData(localeZh);
+      registerLocaleData(localeEnAU);
+    });
+
+    afterAll(() => unregisterLocaleData());
+
+    describe('findLocaleData', () => {
+      it('should throw if the LOCALE_DATA for the chosen locale or its parent locale is not available',
+         () => {
+           expect(() => findLocaleData('pt-AO'))
+               .toThrowError(/Missing locale data for the locale "pt-AO"/);
+         });
+
+      it('should return english data if the locale is en-US',
+         () => { expect(findLocaleData('en-US')).toEqual(localeEn); });
+
+      it('should return the exact LOCALE_DATA if it is available',
+         () => { expect(findLocaleData('fr-CA')).toEqual(localeFrCA); });
+
+      it('should return the parent LOCALE_DATA if it exists and exact locale is not available',
+         () => { expect(findLocaleData('fr-BE')).toEqual(localeFr); });
+
+      it(`should find the LOCALE_DATA even if the locale id is badly formatted`, () => {
+        expect(findLocaleData('ca-ES-VALENCIA')).toEqual(localeCaESVALENCIA);
+        expect(findLocaleData('CA_es_Valencia')).toEqual(localeCaESVALENCIA);
+      });
+
+      it(`should find the LOCALE_DATA if the locale id was registered`, () => {
+        expect(findLocaleData('fake-id')).toEqual(localeFr);
+        expect(findLocaleData('fake_iD')).toEqual(localeFr);
+        expect(findLocaleData('fake-id2')).toEqual(localeFrCA);
+      });
+    });
+  });
+}