Fixes #19916: restore Rack device representation behavior

The select list of 'Images and Label', 'Images Only', and 'Label Only'
was broken during recent work while implementing #19823.

This fixes the issue by placing the `rack_elevation` class attribute on
the <div> element that contains the SVG after being loaded by HTMX. In
addition, we needed to slightly modify the selectors in the frontend
code that looked for the elements within the SVG to hide and/or show.
Previously, it was looking inside of a contentDocument embedded in an
<object> element. The simplified version just looks inside of the
SVG containing div.

netbox/project-static/src/racks.ts

@@ -35,7 +35,7 @@ function showRackElements(
   selector: string,
   elevation: HTMLObjectElement,
 ): void {
-  const elements = elevation.contentDocument?.querySelectorAll(selector) ?? [];
+  const elements = elevation.querySelectorAll(selector) ?? [];
   for (const element of elements) {
     element.classList.remove('hidden');
   }
@@ -45,7 +45,7 @@ function hideRackElements(
   selector: string,
   elevation: HTMLObjectElement,
 ): void {
-  const elements = elevation.contentDocument?.querySelectorAll(selector) ?? [];
+  const elements = elevation.querySelectorAll(selector) ?? [];
   for (const element of elements) {
     element.classList.add('hidden');
   }

netbox/templates/dcim/inc/rack_elevation.html

@@ -1,5 +1,5 @@
 {% load i18n %}
-<div style="margin-left: -30px">
+<div style="margin-left: -30px" class="rack_elevation">
   <div
     hx-get="{% url 'dcim-api:rack-elevation' pk=object.pk %}?face={{ face }}&render=svg{% if extra_params %}&{{ extra_params }}{% endif %}"
     hx-trigger="intersect"