Added entity meta link to reference page

Not totally happy with implementation as is requires extra service to be
injected to core controllers, but does the job.
Included test to cover.
Updated some controller properties to be typed while there.

app/References/ReferenceFetcher.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace BookStack\References;
+
+use BookStack\Auth\Permissions\PermissionApplicator;
+use BookStack\Entities\Models\Entity;
+use BookStack\Entities\Models\Page;
+use Illuminate\Database\Eloquent\Collection;
+use Illuminate\Database\Eloquent\Relations\Relation;
+
+class ReferenceFetcher
+{
+    protected PermissionApplicator $permissions;
+
+    public function __construct(PermissionApplicator $permissions)
+    {
+        $this->permissions = $permissions;
+    }
+
+    /**
+     * Query and return the page references pointing to the given entity.
+     * Loads the commonly required relations while taking permissions into account.
+     */
+    public function getPageReferencesToEntity(Entity $entity): Collection
+    {
+        $baseQuery = $entity->referencesTo()
+            ->where('from_type', '=', (new Page())->getMorphClass())
+            ->with([
+                'from' => fn(Relation $query) => $query->select(Page::$listAttributes),
+                'from.book' => fn(Relation $query) => $query->scopes('visible'),
+                'from.chapter' => fn(Relation $query) => $query->scopes('visible')
+            ]);
+
+        $references = $this->permissions->restrictEntityRelationQuery(
+            $baseQuery,
+            'references',
+            'from_id',
+            'from_type'
+        )->get();
+
+        return $references;
+    }
+
+    /**
+     * Returns the count of page references pointing to the given entity.
+     * Takes permissions into account.
+     */
+    public function getPageReferenceCountToEntity(Entity $entity): int
+    {
+        $baseQuery = $entity->referencesTo()
+            ->where('from_type', '=', (new Page())->getMorphClass());
+
+        $count = $this->permissions->restrictEntityRelationQuery(
+            $baseQuery,
+            'references',
+            'from_id',
+            'from_type'
+        )->count();
+
+        return $count;
+    }
+}