PERF: fast docking of timeline so it does not overlap

In the past we debounced all dock check this causes situations where
sometimes timeline would not dock in time especially on slow computers

This works around it by performing the dock by hand.

Also there was missing integer casting causing over aggressive re-rendering

app/assets/javascripts/discourse/components/topic-timeline.js.es6

@@ -47,6 +47,17 @@ export default MountWidget.extend(Docking, {
     this.queueRerender();
   },
 
+  fastDockCheck(){
+    // we need to dock super fast here, avoid any slow methods
+    // this is not debounced
+    const offset = window.pageYOffset;
+
+    if (offset && this.fastDockAt && offset > this.fastDockAt) {
+      this.fastDockAt = null;
+      $('.timeline-container').addClass('timeline-docked timeline-docked-bottom');
+    }
+  },
+
   dockCheck(info) {
     const mainOffset = $('#main').offset();
     const offsetTop = mainOffset ? mainOffset.top : 0;
@@ -62,13 +73,14 @@ export default MountWidget.extend(Docking, {
 
     this.dockBottom = false;
     if (posTop < topicTop) {
-      this.dockAt = topicTop;
+      this.dockAt = parseInt(topicTop, 10);
     } else if (pos > topicBottom + footerHeight) {
-      this.dockAt = (topicBottom - timelineHeight) + footerHeight;
+      this.dockAt = parseInt((topicBottom - timelineHeight) + footerHeight, 10);
       this.dockBottom = true;
       if (this.dockAt < 0) { this.dockAt = 0; }
     } else {
       this.dockAt = null;
+      this.fastDockAt = parseInt(topicBottom - timelineHeight + footerHeight - offsetTop, 10);
     }
 
     if (this.dockAt !== prev) {

app/assets/javascripts/discourse/mixins/docking.js.es6

@@ -12,6 +12,12 @@ export default Ember.Mixin.create({
   init() {
     this._super();
     this.queueDockCheck = () => {
+
+      // we want to do a very fast non-debounced check first
+      if (this.fastDockCheck) {
+        this.fastDockCheck();
+      }
+
       Ember.run.debounce(this, this.safeDockCheck, 5);
     };
   },