bug #6201 [ChoiceField] Bugfix: Enum translation for Grid (psihius)

This PR was squashed before being merged into the 4.x branch.

Discussion
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[ChoiceField] Bugfix: Enum translation for Grid

The translation array is based on the enum's `name` field, so when choosing translation for the grid, it should also select `name` instead of `value` as the selected value.
This is important when Enum's name and value do not match, like in integer-based enum's or when the case name is not the same as it's value.
Also replaced the array_merge with a foreach that adds data to the array instead of fully rebuilding a new copy of the array with new data.

Commits
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178ecc7 [ChoiceField] Bugfix: Enum translation for Grid

src/Field/Configurator/ChoiceConfigurator.php

@@ -33,6 +33,8 @@ public function configure(FieldDto $field, EntityDto $entityDto, AdminContext $c
         $choicesSupportTranslatableInterface = false;
         $isExpanded = true === $field->getCustomOption(ChoiceField::OPTION_RENDER_EXPANDED);
         $isMultipleChoice = true === $field->getCustomOption(ChoiceField::OPTION_ALLOW_MULTIPLE_CHOICES);
+        // Initialize the variable since we are using it outside the $enumsAreSupported condition
+        $allChoicesAreEnums = false;
 
         $choices = $this->getChoices($field->getCustomOption(ChoiceField::OPTION_CHOICES), $entityDto, $field);
 
@@ -132,7 +134,8 @@ public function configure(FieldDto $field, EntityDto $entityDto, AdminContext $c
         $flippedChoices = $areChoicesTranslatable ? $choices : array_flip($this->flatten($choices));
         foreach ((array) $fieldValue as $selectedValue) {
             $selectedValue = match (true) {
-                $selectedValue instanceof \BackedEnum => $selectedValue->value,
+                // We check if $allChoicesAreEnums is true for enum's and choices array is generated using ->name as index
+                $selectedValue instanceof \BackedEnum => $allChoicesAreEnums && $choicesSupportTranslatableInterface ? $selectedValue->name : $selectedValue->value,
                 $selectedValue instanceof \UnitEnum => $selectedValue->name,
                 default => $selectedValue
             };
@@ -198,7 +201,9 @@ private function flatten(array $choices): array
         foreach ($choices as $label => $choice) {
             // Flatten grouped choices
             if (\is_array($choice)) {
-                $flattened = array_merge($flattened, $choice);
+                foreach ($choice as $subLabel => $subChoice) {
+                    $flattened[$subLabel] = $subChoice;
+                }
             } elseif ($choice instanceof \BackedEnum) {
                 $flattened[$choice->name] = $choice->value;
             } elseif ($choice instanceof \UnitEnum) {