fix(moment-adapter): incorrectly deserializing moment dates and not setting locale on deserialized values (#14685)

Fixes a couple of issues I noticed while doing the Luxon adapter:
* If a `Moment` instance was passed in to `deserialize`, we were returning a new `Moment` instance set to the current date/time, rather than the ones from the passed-in object.
* In some cases the object returned by `deserialize` didn't have its locale set to the one from the adapter.

Author: crisbeto

src/material-moment-adapter/adapter/moment-date-adapter.spec.ts

@@ -333,6 +333,19 @@ describe('MomentDateAdapter', () => {
     assertValidDate(adapter.deserialize(moment.invalid()), false);
   });
 
+  it('should clone the date when deserializing a Moment date', () => {
+    let date = moment([2017, JAN, 1]);
+    expect(adapter.deserialize(date)!.format()).toEqual(date.format());
+    expect(adapter.deserialize(date)).not.toBe(date);
+  });
+
+  it('should deserialize dates with the correct locale', () => {
+    adapter.setLocale('ja');
+    expect(adapter.deserialize('1985-04-12T23:20:50.52Z')!.locale()).toBe('ja');
+    expect(adapter.deserialize(new Date())!.locale()).toBe('ja');
+    expect(adapter.deserialize(moment())!.locale()).toBe('ja');
+  });
+
   it('setLocale should not modify global moment locale', () => {
     expect(moment.locale()).toBe('en');
     adapter.setLocale('ja-JP');

src/material-moment-adapter/adapter/moment-date-adapter.ts

@@ -211,7 +211,10 @@ export class MomentDateAdapter extends DateAdapter<Moment> {
   deserialize(value: any): Moment | null {
     let date;
     if (value instanceof Date) {
-      date = this._createMoment(value);
+      date = this._createMoment(value).locale(this.locale);
+    } else if (this.isDateInstance(value)) {
+      // Note: assumes that cloning also sets the correct locale.
+      return this.clone(value);
     }
     if (typeof value === 'string') {
       if (!value) {
@@ -220,7 +223,7 @@ export class MomentDateAdapter extends DateAdapter<Moment> {
       date = this._createMoment(value, moment.ISO_8601).locale(this.locale);
     }
     if (date && this.isValid(date)) {
-      return date;
+      return this._createMoment(date).locale(this.locale);
     }
     return super.deserialize(value);
   }