This was failing quite often with the following error:
```
1) Emoji deny list when using composer should remove denied emojis from emoji picker
Failure/Error: find("#{COMPOSER_ID} .emoji-picker")
Capybara::ElementNotFound:
Unable to find css "#reply-control .emoji-picker"
```
This was because our `click_toolbar_button` call on the Composer
page object used a number for the position of the toolbar button,
which can be flaky since there are things that hide/show toolbar
buttons or change their position.
Each toolbar button in the composer has a CSS class, so it is
more reliable to use that instead. Also fixed an instance of
calling `has_X?` method directly instead of using the
`have_x` rspec matcher.
30f0afe873