UX: enhances chat copy features (#23770)

- Allows to copy quotes from mobile
- Allows to copy text of a message from mobile
- Allows to select messages by clicking on it when selection has started

Note this commit is also now using toasts to show a confirmation of copy, and refactors system specs helpers concerning secondary actions.

<!-- NOTE: All pull requests should have tests (rspec in Ruby, qunit in JavaScript). If your code does not include test coverage, please include an explanation of why it was omitted. -->

plugins/chat/spec/system/transcript_spec.rb

@@ -20,7 +20,9 @@ RSpec.describe "Quoting chat message transcripts", type: :system do
     messages = Array.wrap(messages)
     messages.each { |message| channel_page.messages.select(message) }
     channel_page.selection_management.copy
-    expect(page).to have_css(".chat-selection-management[data-last-copy-successful]")
+    expect(PageObjects::Components::Toasts.new).to have_success(
+      I18n.t("js.chat.quote.copy_success"),
+    )
     clip_text = cdp.read_clipboard
     expect(clip_text.chomp).to eq(generate_transcript(messages, current_user))
     clip_text