FIX: Make scrolling to bottom post in topic more consistent (#8671)

* Make scrolling to bottom post in topic more consistent

* when using the slider to scroll past the bottom post,
  we now scroll to the bottom of the post/page IF the
  post height is > the window height (e.g. really long
  posts). if the post height is smaller, then we lock
  onto and jump to the top of the post
* this also removes the mobile hack that would always jump
  to the top of the last post on mobile

* Prettier lint

app/assets/javascripts/discourse/lib/url.js.es6

@@ -99,9 +99,18 @@ const DiscourseURL = EmberObject.extend({
       let holder;
 
       if (opts.jumpEnd) {
-        $(window).scrollTop($(document).height() - $(window).height());
-        _transitioning = false;
-        return;
+        let $holder = $(holderId);
+        let holderHeight = $holder.height();
+        let windowHeight = $(window).height() - offsetCalculator();
+
+        // scroll to the bottom of the post and stop any further action if the
+        // post is yuge, otherwise just jump to the top of the post
+        // using the lock & holder method
+        if (holderHeight > windowHeight) {
+          $(window).scrollTop($holder.offset().top + holderHeight);
+          _transitioning = false;
+          return;
+        }
       }
 
       if (postNumber === 1 && !opts.anchor) {

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

@@ -263,7 +263,7 @@ createWidget("timeline-scrollarea", {
     const position = this.position();
     this.state.scrolledPost = position.current;
 
-    if (position.current === position.scrollPosition || this.site.mobileView) {
+    if (position.current === position.scrollPosition) {
       this.sendWidgetAction("jumpToIndex", position.current);
     } else {
       this.sendWidgetAction("jumpEnd");