DEV: Speed up core system tests (#21394)

What is the problem?

We are relying on RSpec custom matchers in system tests by defining
predicates in page objects. The problem is that this can result in a
system test unnecessarily waiting up till the full duration of
Capybara's default wait time when the RSpec custom matcher is used with
`not_to`. Considering this topic page object where we have a `has_post?`
predicate defined.

```
class Topic < PageObject
  def has_post?
    has_css?('something')
  end
end
```

The assertion `expect(Topic.new).not_to have_post` will end up waiting
the full Capybara's default wait time since the RSpec custom matcher is
calling Capybara's `has_css?` method which will wait until the selector
appear. If the selector has already disappeared by the time the
assertion is called, we end up waiting for something that will never
exists.

This commit fixes such cases by introducing new predicates that uses
the `has_no_*` versions of Capybara's node matchers.

For future reference, `to have_css` and `not_to have_css` is safe to sue
because the RSpec matcher defined by Capbyara is smart enough to call
`has_css?` or `has_no_css?` based on the expectation of the assertion.

spec/system/page_objects/components/composer.rb

@@ -76,12 +76,26 @@ module PageObjects
         has_css?(AUTOCOMPLETE_MENU)
       end
 
+      def has_no_emoji_autocomplete?
+        has_no_css?(AUTOCOMPLETE_MENU)
+      end
+
+      EMOJI_SUGGESTION_SELECTOR = "#{AUTOCOMPLETE_MENU} .emoji-shortname"
+
       def has_emoji_suggestion?(emoji)
-        has_css?("#{AUTOCOMPLETE_MENU} .emoji-shortname", text: emoji)
+        has_css?(EMOJI_SUGGESTION_SELECTOR, text: emoji)
+      end
+
+      def has_no_emoji_suggestion?(emoji)
+        has_no_css?(EMOJI_SUGGESTION_SELECTOR, text: emoji)
       end
 
       def has_emoji_preview?(emoji)
-        page.has_css?(".d-editor-preview .emoji[title=':#{emoji}:']")
+        page.has_css?(emoji_preview_selector(emoji))
+      end
+
+      def has_no_emoji_preview?(emoji)
+        page.has_no_css?(emoji_preview_selector(emoji))
       end
 
       def composer_input
@@ -91,6 +105,12 @@ module PageObjects
       def composer_popup
         find("#{COMPOSER_ID} .composer-popup")
       end
+
+      private
+
+      def emoji_preview_selector(emoji)
+        ".d-editor-preview .emoji[title=':#{emoji}:']"
+      end
     end
   end
 end