Added content-view body classes generated from tags

Included tests to cover.

Closes #3583

app/Actions/TagClassGenerator.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace BookStack\Actions;
+
+class TagClassGenerator
+{
+
+    protected array $tags;
+
+    /**
+     * @param Tag[] $tags
+     */
+    public function __construct(array $tags)
+    {
+        $this->tags = $tags;
+    }
+
+    /**
+     * @return string[]
+     */
+    public function generate(): array
+    {
+        $classes = [];
+
+        foreach ($this->tags as $tag) {
+            $name = $this->normalizeTagClassString($tag->name);
+            $value = $this->normalizeTagClassString($tag->value);
+            $classes[] = 'tag-name-' . $name;
+            if ($value) {
+                $classes[] = 'tag-value-' . $value;
+                $classes[] = 'tag-pair-' . $name . '-' . $value;
+            }
+        }
+
+        return array_unique($classes);
+    }
+
+    public function generateAsString(): string
+    {
+        return implode(' ', $this->generate());
+    }
+
+    protected function normalizeTagClassString(string $value): string
+    {
+        $value = str_replace(' ', '', strtolower($value));
+        $value = str_replace('-', '', strtolower($value));
+        return $value;
+    }
+
+}