FEATURE: New Discourse Lightbox using Glimmer (#19798)

Introduces new lightbox as a step to migrate away from Magnific Popup.

Please see https://meta.discourse.org/t/migrating-away-from-magnific-popup/251505 for more details

Co-authored-by: Nat <natalie.tay@discourse.org>
Co-authored-by: David Battersby <info@davidbattersby.com>

lib/svg_sprite.rb

@@ -149,6 +149,7 @@ module SvgSprite
         hourglass-start
         id-card
         image
+        images
         inbox
         info-circle
         italic
@@ -187,6 +188,8 @@ module SvgSprite
         reply
         rocket
         search
+        search-plus
+        search-minus
         share
         shield-alt
         sign-in-alt