Extracted icon helper, aligned container resolution

Also updated breadcrumb view composer to current standards.
Closes #4553

app/Util/SvgIcon.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace BookStack\Util;
+
+class SvgIcon
+{
+    public function __construct(
+        protected string $name,
+        protected array $attrs = []
+    ) {
+    }
+
+    public function toHtml(): string
+    {
+        $attrs = array_merge([
+            'class'     => 'svg-icon',
+            'data-icon' => $this->name,
+            'role'      => 'presentation',
+        ], $this->attrs);
+
+        $attrString = ' ';
+        foreach ($attrs as $attrName => $attr) {
+            $attrString .= $attrName . '="' . $attr . '" ';
+        }
+
+        $iconPath = resource_path('icons/' . $this->name . '.svg');
+        $themeIconPath = theme_path('icons/' . $this->name . '.svg');
+
+        if ($themeIconPath && file_exists($themeIconPath)) {
+            $iconPath = $themeIconPath;
+        } elseif (!file_exists($iconPath)) {
+            return '';
+        }
+
+        $fileContents = file_get_contents($iconPath);
+
+        return str_replace('<svg', '<svg' . $attrString, $fileContents);
+    }
+}