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/ReferenceStore.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace BookStack\References;
+
+use BookStack\Entities\Models\Page;
+use Illuminate\Database\Eloquent\Collection;
+
+class ReferenceStore
+{
+
+    /**
+     * Update the outgoing references for the given page.
+     */
+    public function updateForPage(Page $page): void
+    {
+        $this->updateForPages([$page]);
+    }
+
+    /**
+     * Update the outgoing references for all pages in the system.
+     */
+    public function updateForAllPages(): void
+    {
+        Reference::query()
+            ->where('from_type', '=', (new Page())->getMorphClass())
+            ->delete();
+
+        Page::query()->select(['id', 'html'])->chunk(100, function(Collection $pages) {
+            $this->updateForPages($pages->all());
+        });
+    }
+
+    /**
+     * Update the outgoing references for the pages in the given array.
+     *
+     * @param Page[] $pages
+     */
+    protected function updateForPages(array $pages): void
+    {
+        if (count($pages) === 0) {
+            return;
+        }
+
+        $parser = CrossLinkParser::createWithEntityResolvers();
+        $references = [];
+
+        $pageIds = array_map(fn(Page $page) => $page->id, $pages);
+        Reference::query()
+            ->where('from_type', '=', $pages[0]->getMorphClass())
+            ->whereIn('from_id', $pageIds)
+            ->delete();
+
+        foreach ($pages as $page) {
+            $models = $parser->extractLinkedModels($page->html);
+
+            foreach ($models as $model) {
+                $references[] = [
+                    'from_id' => $page->id,
+                    'from_type' => $page->getMorphClass(),
+                    'to_id' => $model->id,
+                    'to_type' => $model->getMorphClass(),
+                ];
+            }
+        }
+
+        foreach (array_chunk($references, 1000) as $referenceDataChunk) {
+            Reference::query()->insert($referenceDataChunk);
+        }
+    }
+
+}