DEV: Upgrade Ember to version 3.12.2 (#8753)

* DEV: Use Ember 3.12.2
* Add Ember version to ThemeField's DEPENDENT_CONSTANTS
* DEV: Use `id` instead of `elementId` (See: https://github.com/emberjs/ember.js/issues/18147)
* FIX: Don't leak event listeners (bug introduced in 999e2ff)

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

@@ -111,6 +111,8 @@ export default MountWidget.extend(Docking, {
   },
 
   willDestroyElement() {
+    this._super(...arguments);
+
     if (!this.site.mobileView) {
       this.appEvents.off("composer:opened", this, this.queueRerender);
       this.appEvents.off("composer:resized", this, this.queueRerender);

app/assets/javascripts/pretty-text/emoji.js.es6

@@ -126,8 +126,6 @@ export function performEmojiUnescape(string, opts) {
         } alt='${emojiVal}' class='${classes}'>`
       : m;
   });
-
-  return string;
 }
 
 export function performEmojiEscape(string, opts) {
@@ -145,8 +143,6 @@ export function performEmojiEscape(string, opts) {
 
     return m;
   });
-
-  return string;
 }
 
 export function isCustomEmoji(code, opts) {

app/assets/javascripts/wizard/templates/components/wizard-field-dropdown.hbs

@@ -1,5 +1,5 @@
 {{combo-box
-  elementId=field.id
+  id=field.id
   class=fieldClass
   value=field.value
   content=field.choices

app/assets/javascripts/wizard/templates/components/wizard-field-text.hbs

@@ -1 +1 @@
-{{input elementId=field.id value=field.value class=fieldClass placeholder=field.placeholder tabindex="9"}}
+{{input id=field.id value=field.value class=fieldClass placeholder=field.placeholder tabindex="9"}}

app/assets/javascripts/wizard/templates/components/wizard-field-textarea.hbs

@@ -1 +1 @@
-{{textarea elementId=field.id value=field.value class=fieldClass placeholder=field.placeholder tabindex="9"}}
+{{textarea id=field.id value=field.value class=fieldClass placeholder=field.placeholder tabindex="9"}}

app/models/theme_field.rb

@@ -61,8 +61,11 @@ class ThemeField < ActiveRecord::Base
                    if: Proc.new { |field| ThemeField.theme_var_type_ids.include?(field.type_id) }
 
   BASE_COMPILER_VERSION = 14
-  DEPENDENT_CONSTANTS = [BASE_COMPILER_VERSION,
-                        GlobalSetting.cdn_url]
+  DEPENDENT_CONSTANTS = [
+    BASE_COMPILER_VERSION,
+    Ember::VERSION,
+    GlobalSetting.cdn_url
+  ]
   COMPILER_VERSION = Digest::SHA1.hexdigest(DEPENDENT_CONSTANTS.join)
 
   belongs_to :theme