FIX: generates markdown from pasting link (#21241)

After removing `TextareaTextManipulation` from `ChatComposer` and using `TextareaInteractor` as a proxy, one function has been forgotten: `paste(event)` which is not available in glimmer components anymore, and even less avaiable now that the mixin is not tied to a component anymore but a real DOM node. As a solution we now add a manual paste event listener which will call `paste(event)`.

plugins/chat/spec/system/chat_composer_spec.rb

@@ -262,4 +262,35 @@ RSpec.describe "Chat composer", type: :system, js: true do
       expect(find(".chat-composer__input").value).to eq("bb")
     end
   end
+
+  context "when pasting link over selected text" do
+    before do
+      channel_1.add(current_user)
+      sign_in(current_user)
+    end
+
+    it "outputs a markdown link" do
+      modifier = /darwin/i =~ RbConfig::CONFIG["host_os"] ? :command : :control
+      select_text = <<-JS
+        const element = document.querySelector(arguments[0]);
+        element.focus();
+        element.setSelectionRange(0, element.value.length)
+      JS
+
+      chat.visit_channel(channel_1)
+
+      find("body").send_keys("https://www.discourse.org")
+      page.execute_script(select_text, ".chat-composer__input")
+
+      page.send_keys [modifier, "c"]
+      page.send_keys [:backspace]
+
+      find("body").send_keys("discourse")
+      page.execute_script(select_text, ".chat-composer__input")
+
+      page.send_keys [modifier, "v"]
+
+      expect(find(".chat-composer__input").value).to eq("[discourse](https://www.discourse.org)")
+    end
+  end
 end