Fix customer autocomplete filter not displaying guest customers (#18980)

Guest customers (without first/last name) appeared as blank entries in the
order grid's customer autocomplete filter, making them impossible to select.

Added `getNameOrEmail()` to `CustomerInterface` which returns
`"Full Name (email)"` for named customers and just the email for guests,
and switched the order grid filter to use it as its choice label.

src/Sylius/Bundle/AdminBundle/Resources/config/grids/order.yml

@@ -114,7 +114,7 @@ sylius_grid:
                     form_options:
                         extra_options:
                             class: '%sylius.model.customer.class%'
-                            choice_label: fullname
+                            choice_label: nameOrEmail
                 date:
                     type: date
                     label: sylius.ui.date

src/Sylius/Component/Customer/Model/Customer.php

@@ -89,6 +89,17 @@ class Customer implements CustomerInterface, \Stringable
         return trim(sprintf('%s %s', $this->firstName, $this->lastName));
     }
 
+    public function getNameOrEmail(): string
+    {
+        $fullName = $this->getFullName();
+
+        if ('' !== $fullName) {
+            return sprintf('%s (%s)', $fullName, $this->email);
+        }
+
+        return (string) $this->email;
+    }
+
     public function getFirstName(): ?string
     {
         return $this->firstName;

src/Sylius/Component/Customer/Model/CustomerInterface.php

@@ -37,6 +37,8 @@ interface CustomerInterface extends TimestampableInterface, ResourceInterface
 
     public function getFullName(): string;
 
+    public function getNameOrEmail(): string;
+
     public function getFirstName(): ?string;
 
     public function setFirstName(?string $firstName): void;