Add Mongo builder mixin to DocumentModel

It helps with autocompletion as IDEs will recognize Mongo builder
methods that are not present on the base builder.

Author: paulinevos

src/Eloquent/Builder.php

@@ -69,7 +69,7 @@ class Builder extends EloquentBuilder
     ];
 
     /**
-     * @return ($function is null ? AggregationBuilder : self)
+     * @return ($function is null ? AggregationBuilder : $this)
      *
      * @inheritdoc
      */

src/Eloquent/DocumentModel.php

@@ -50,6 +50,7 @@
 use function strlen;
 use function var_export;
 
+/** @mixin Builder */
 trait DocumentModel
 {
     use HybridRelations;

tests/Models/Anniversary.php

@@ -6,16 +6,10 @@
 
 use Illuminate\Database\Eloquent\Model;
 use MongoDB\Laravel\Eloquent\DocumentModel;
-use MongoDB\Laravel\Eloquent\Model as Eloquent;
-use MongoDB\Laravel\Query\Builder;
 
 /**
  * @property string $name
  * @property string $anniversary
- * @mixin Eloquent
- * @method static Builder create(...$values)
- * @method static Builder truncate()
- * @method static Eloquent sole(...$parameters)
  */
 class Anniversary extends Model
 {

tests/Models/HiddenAnimal.php

@@ -6,17 +6,11 @@
 
 use Illuminate\Database\Eloquent\Model;
 use MongoDB\Laravel\Eloquent\DocumentModel;
-use MongoDB\Laravel\Eloquent\Model as Eloquent;
-use MongoDB\Laravel\Query\Builder;
 
 /**
  * @property string $name
  * @property string $country
  * @property bool $can_be_eaten
- * @mixin Eloquent
- * @method static Builder create(...$values)
- * @method static Builder truncate()
- * @method static Eloquent sole(...$parameters)
  */
 final class HiddenAnimal extends Model
 {