FIX: delay custom section reorder (#20781)

Reorder should start after 300ms.
In addition, pointer events should be blocked to not open link after reorder is finished.

app/assets/javascripts/discourse-common/addon/config/environment.js

@@ -13,7 +13,7 @@ export function setEnvironment(e) {
 }
 
 export function isTesting() {
-  return environment === "testing";
+  return environment === "testing" || environment === "test";
 }
 
 // Generally means "before we migrated to Ember CLI"

app/assets/javascripts/discourse/app/components/sidebar/user/section-link.js

@@ -1,6 +1,7 @@
 import { tracked } from "@glimmer/tracking";
 import { bind } from "discourse-common/utils/decorators";
 import RouteInfoHelper from "discourse/lib/sidebar/route-info-helper";
+import { isTesting } from "discourse-common/config/environment";
 
 export default class SectionLink {
   @tracked linkDragCss;
@@ -22,8 +23,25 @@ export default class SectionLink {
   }
 
   @bind
-  didStartDrag(e) {
-    this.mouseY = e.screenY;
+  didStartDrag(event) {
+    // 0 represents left button of the mouse
+    if (event.button === 0) {
+      this.willDrag = true;
+      setTimeout(
+        () => {
+          this.delayedStart(event);
+        },
+        isTesting() ? 0 : 300
+      );
+    }
+  }
+  delayedStart(event) {
+    if (this.willDrag) {
+      this.mouseY = event.screenY;
+      this.linkDragCss = "drag";
+      this.section.disable();
+      this.drag = true;
+    }
   }
 
   @bind
@@ -32,11 +50,16 @@ export default class SectionLink {
     this.mouseY = null;
     this.section.enable();
     this.section.reorder();
+    this.willDrag = false;
+    this.drag = false;
   }
 
   @bind
-  dragMove(e) {
-    const currentMouseY = e.screenY;
+  dragMove(event) {
+    if (!this.drag) {
+      return;
+    }
+    const currentMouseY = event.screenY;
     const distance = currentMouseY - this.mouseY;
     if (!this.linkHeight) {
       this.linkHeight = document.getElementsByClassName(
@@ -55,7 +78,5 @@ export default class SectionLink {
         this.mouseY = currentMouseY;
       }
     }
-    this.linkDragCss = "drag";
-    this.section.disable();
   }
 }

app/assets/stylesheets/common/base/sidebar-custom-section.scss

@@ -16,6 +16,9 @@
   }
 
   .sidebar-section-wrapper.disabled {
+    a {
+      pointer-events: none;
+    }
     .sidebar-section-link-wrapper {
       .sidebar-section-link-prefix.icon,
       .sidebar-section-link {