fix(material/chips): chip input with autocomplete has both the selected and the suggested values added

Fixes a bug in the Angular Material `chips` component where the autocomplete input
has both the selected and the suggested values added.
The input should only take the suggested value

Fixes #28852

Author: lsamboretrorabbit

src/material/chips/chip-input.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {BACKSPACE, hasModifierKey} from '@angular/cdk/keycodes';
+import {BACKSPACE, ENTER, hasModifierKey} from '@angular/cdk/keycodes';
 import {
   AfterContentInit,
   Directive,
@@ -167,6 +167,10 @@ export class MatChipInput implements MatChipTextControl, AfterContentInit, OnCha
         this._chipGrid._focusLastChip();
         event.preventDefault();
         return;
+      } else if (event.keyCode === ENTER) {
+        // Prevent adding both the search string and the selected suggestion
+        event.preventDefault();
+        return;
       } else {
         this._focusLastChipOnBackspace = false;
       }