fix(material/checkbox): focus not moved to input when clicking on tou…

…ch target

Fixes that while we were toggling the checked state of a checkbox when its touch target is clicked, we weren't moving focus to the internal `input`.

Fixes #26486.

src/material/checkbox/checkbox.ts

@@ -380,6 +380,9 @@ export abstract class _MatCheckboxBase<E>
         });
       }
 
+      // Normally the input should be focused already, but if the click comes from something
+      // like the touch target, then we might have to focus it ourselves.
+      this._inputElement.nativeElement.focus();
       this._checked = !this._checked;
       this._transitionCheckState(
         this._checked ? TransitionCheckState.Checked : TransitionCheckState.Unchecked,