PERF: Improve rendering performance of empty PluginOutlets (#23165)

This commit introduces a 'shortcut' when rendering PluginOutlets which have no registered connectors. On my machine, this improves rendering performance of empty PluginOutlets by around 30-40% (tested by running tachometer on a `/latest` route with 600 plugin outlets).

app/assets/javascripts/discourse/app/components/plugin-outlet.hbs

@@ -22,7 +22,7 @@
       {{/if}}
     {{/each}}
   </this.wrapperComponent>
-{{else}}
+{{else if this.connectorsExist}}
   {{! The modern path: no wrapper element = no classic component }}
   {{#each this.connectors as |c|}}
     {{#if c.componentClass}}

app/assets/javascripts/discourse/app/components/plugin-outlet.js

@@ -3,6 +3,7 @@ import ClassicComponent from "@ember/component";
 
 import {
   buildArgsWithDeprecations,
+  connectorsExist,
   renderedConnectorsFor,
 } from "discourse/lib/plugin-connectors";
 import { helperContext } from "discourse-common/lib/helpers";
@@ -86,6 +87,10 @@ export default class PluginOutletComponent extends GlimmerComponentWithDeprecate
     );
   }
 
+  get connectorsExist() {
+    return connectorsExist(this.args.name);
+  }
+
   // Traditionally, pluginOutlets had an argument named 'args'. However, that name is reserved
   // in recent versions of ember so we need to migrate to outletArgs
   @cached

app/assets/javascripts/discourse/app/lib/plugin-connectors.js

@@ -165,6 +165,13 @@ function buildConnectorCache() {
   }
 }
 
+export function connectorsExist(outletName) {
+  if (!_connectorCache) {
+    buildConnectorCache();
+  }
+  return Boolean(_connectorCache[outletName]);
+}
+
 export function connectorsFor(outletName) {
   if (!_connectorCache) {
     buildConnectorCache();