Focus editor after calling fill_in_rich_text_area

When System Tests call `fill_in_rich_text_area`, they interact with
`<trix-editor>` elements by changing the contents programmatically.

This is unlike how end-users will interact with the element. Overhauling
the test helper to more accurately reflect Real World usage would
require a sizable effort.

With that being said, leaving the `<trix-editor>` with focus after
populating its contents is a minor change that makes it a more genuine
recreation.

actiontext/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Focus rich-text editor after calling `fill_in_rich_text_area`
+
+    *Sean Doyle*
+
 *   Support `strict_loading:` option for `has_rich_text` declaration
 
     *Sean Doyle*

actiontext/lib/action_text/system_test_helper.rb

@@ -30,7 +30,11 @@ module SystemTestHelper
     #   # <trix-editor input="trix_input_1"></trix-editor>
     #   fill_in_rich_text_area "message[content]", with: "Hello <em>world!</em>"
     def fill_in_rich_text_area(locator = nil, with:)
-      find(:rich_text_area, locator).execute_script("this.editor.loadHTML(arguments[0])", with.to_s)
+      javascript = <<~JS
+        this.editor.loadHTML(arguments[0])
+        this.editor.focus()
+      JS
+      find(:rich_text_area, locator).execute_script(javascript, with.to_s)
     end
   end
 end

actiontext/test/system/system_test_helper_test.rb

@@ -3,6 +3,14 @@
 require "application_system_test_case"
 
 class ActionText::SystemTestHelperTest < ApplicationSystemTestCase
+  test "filling in a rich-text area focuses the trix-editor" do
+    visit new_message_url
+
+    fill_in_rich_text_area "message_content", with: "Hello world!"
+
+    assert_selector(:rich_text_area, "message[content]", &:focused?)
+  end
+
   test "filling in a rich-text area by ID" do
     visit new_message_url
     assert_selector "trix-editor#message_content"