Allow groupBy to work with enums. (#17574)

Allow groupBy() to work with enums.

Remove exception for unit enums for indexBy().

CollectionTrait.php

@@ -292,6 +292,12 @@ public function groupBy(callable|string $path): CollectionInterface
                     'Use a callback to return a default value for that path.'
                 );
             }
+            if ($pathValue instanceof BackedEnum) {
+                $pathValue = $pathValue->value;
+            } elseif ($pathValue instanceof UnitEnum) {
+                $pathValue = $pathValue->name;
+            }
+
             $group[$pathValue][] = $value;
         }
 
@@ -313,6 +319,12 @@ public function indexBy(callable|string $path): CollectionInterface
                     'Use a callback to return a default value for that path.'
                 );
             }
+            if ($pathValue instanceof BackedEnum) {
+                $pathValue = $pathValue->value;
+            } elseif ($pathValue instanceof UnitEnum) {
+                $pathValue = $pathValue->name;
+            }
+
             $group[$pathValue] = $value;
         }
 
@@ -617,7 +629,7 @@ public function combine(
                 if ($mapKey instanceof BackedEnum) {
                     $mapKey = $mapKey->value;
                 } elseif ($mapKey instanceof UnitEnum) {
-                    throw new InvalidArgumentException('Cannot index by path that is a non-backed enum.');
+                    $mapKey = $mapKey->name;
                 }
 
                 $mapReduce->emit($rowVal($value, $key), $mapKey);