Make issuable sidebar setSidebarHeight more efficient

1. Moves logic for setSidebarHeight into sidebar_height_manager to allow for better code sharing with bulk update sidebar.
2. Makes setSidebarHeight more efficient, by preventing its being called when sidebar state hasn't changed.

app/assets/javascripts/right_sidebar.js

@@ -9,6 +9,8 @@ import Cookies from 'js-cookie';
       this.sidebar = $('aside');
       this.removeListeners();
       this.addEventListeners();
+      this.$navHeight = $('.navbar-gitlab').outerHeight() + $('.layout-nav').outerHeight() + $('.sub-nav-scroll').outerHeight();
+      this.$rightSidebar = $('.js-right-sidebar');
     }
 
     Sidebar.prototype.removeListeners = function () {
@@ -21,14 +23,14 @@ import Cookies from 'js-cookie';
 
     Sidebar.prototype.addEventListeners = function() {
       const $document = $(document);
-      const throttledSetSidebarHeight = _.throttle(this.setSidebarHeight, 10);
+      const throttledSetSidebarHeight = _.throttle(this.setSidebarHeight.bind(this), 300);
 
       this.sidebar.on('click', '.sidebar-collapsed-icon', this, this.sidebarCollapseClicked);
       $('.dropdown').on('hidden.gl.dropdown', this, this.onSidebarDropdownHidden);
       $('.dropdown').on('loading.gl.dropdown', this.sidebarDropdownLoading);
       $('.dropdown').on('loaded.gl.dropdown', this.sidebarDropdownLoaded);
+      $(window).on('scroll', () => throttledSetSidebarHeight());
       $(window).on('resize', () => throttledSetSidebarHeight());
-      $document.on('scroll', () => throttledSetSidebarHeight());
       $document.on('click', '.js-sidebar-toggle', function(e, triggered) {
         var $allGutterToggleIcons, $this, $thisIcon;
         e.preventDefault();
@@ -207,13 +209,16 @@ import Cookies from 'js-cookie';
     };
 
     Sidebar.prototype.setSidebarHeight = function() {
-      const $navHeight = $('.navbar-gitlab').outerHeight() + $('.layout-nav').outerHeight() + $('.sub-nav-scroll').outerHeight();
-      const $rightSidebar = $('.js-right-sidebar');
-      const diff = $navHeight - $(window).scrollTop();
+      const currentScrollDepth = window.pageYOffset || 0;
+      const diff = this.$navHeight - currentScrollDepth;
+
       if (diff > 0) {
-        $rightSidebar.outerHeight($(window).height() - diff);
-      } else {
-        $rightSidebar.outerHeight('100%');
+        const newSidebarHeight = window.innerHeight - diff;
+        this.$rightSidebar.outerHeight(newSidebarHeight);
+        this.sidebarHeightIsCustom = true;
+      } else if (this.sidebarHeightIsCustom) {
+        this.$rightSidebar.outerHeight('100%');
+        this.sidebarHeightIsCustom = false;
       }
     };