FIX: Clear theme caches after database transaction has committed

This was causing unusual side effects on high-traffic sites, where the cache would be rebuilt before the transaction had been committed

app/models/theme.rb

@@ -68,7 +68,7 @@ class Theme < ActiveRecord::Base
 
     remove_from_cache!
     clear_cached_settings!
-    ColorScheme.hex_cache.clear
+    DB.after_commit { ColorScheme.hex_cache.clear }
     notify_theme_change(with_scheme: notify_with_scheme)
   end
 
@@ -270,7 +270,9 @@ class Theme < ActiveRecord::Base
   end
 
   def self.clear_cache!
-    @cache.clear
+    DB.after_commit do
+      @cache.clear
+    end
   end
 
   def self.targets
@@ -302,8 +304,10 @@ class Theme < ActiveRecord::Base
   end
 
   def notify_theme_change(with_scheme: false)
-    theme_ids = Theme.transform_ids([id])
-    self.class.notify_theme_change(theme_ids, with_scheme: with_scheme)
+    DB.after_commit do
+      theme_ids = Theme.transform_ids([id])
+      self.class.notify_theme_change(theme_ids, with_scheme: with_scheme)
+    end
   end
 
   def self.refresh_message_for_targets(targets, theme_ids)
@@ -474,7 +478,9 @@ class Theme < ActiveRecord::Base
   end
 
   def clear_cached_settings!
-    Discourse.cache.delete("settings_for_theme_#{self.id}")
+    DB.after_commit do
+      Discourse.cache.delete("settings_for_theme_#{self.id}")
+    end
   end
 
   def included_settings

app/models/theme_field.rb

@@ -317,23 +317,23 @@ class ThemeField < ActiveRecord::Base
       self.value_baked, self.error = translation_field? ? process_translation : process_html(self.value)
       self.error = nil unless self.error.present?
       self.compiler_version = COMPILER_VERSION
-      CSP::Extension.clear_theme_extensions_cache!
+      DB.after_commit { CSP::Extension.clear_theme_extensions_cache! }
     elsif extra_js_field?
       self.value_baked, self.error = process_extra_js(self.value)
       self.error = nil unless self.error.present?
       self.compiler_version = COMPILER_VERSION
     elsif basic_scss_field?
       ensure_scss_compiles!
-      Stylesheet::Manager.clear_theme_cache!
+      DB.after_commit { Stylesheet::Manager.clear_theme_cache! }
     elsif settings_field?
       validate_yaml!
       theme.clear_cached_settings!
-      CSP::Extension.clear_theme_extensions_cache!
-      SvgSprite.expire_cache
+      DB.after_commit { CSP::Extension.clear_theme_extensions_cache! }
+      DB.after_commit { SvgSprite.expire_cache }
       self.value_baked = "baked"
       self.compiler_version = COMPILER_VERSION
     elsif svg_sprite_field?
-      SvgSprite.expire_cache
+      DB.after_commit { SvgSprite.expire_cache }
       self.error = nil
       self.value_baked = "baked"
       self.compiler_version = COMPILER_VERSION