Use includes instead of eager_load for with_all_rich_text

`eager_load` performs a single query using a `LEFT OUTER JOIN` to load
the associations. Loading the associations in a join can result in many
rows that contain redundant data and it performs poorly at scale.

With `includes` a separate query is performed for each association,
unless a join is required by conditions.

Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

actiontext/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Use `includes` instead of `eager_load` for `with_all_rich_text`.
+
+    *Petrik de Heus*
+
 *   Delegate `ActionText::Content#deconstruct` to `Nokogiri::XML::DocumentFragment#elements`
 
     ```ruby

actiontext/lib/action_text/attribute.rb

@@ -65,7 +65,7 @@ def #{name}=(body)
 
       # Eager load all dependent RichText models in bulk.
       def with_all_rich_text
-        eager_load(rich_text_association_names)
+        includes(rich_text_association_names)
       end
 
       def rich_text_association_names

actiontext/test/unit/model_test.rb

@@ -106,9 +106,18 @@ class ActionText::ModelTest < ActiveSupport::TestCase
   end
 
   test "eager loading all rich text" do
-    Message.create!(subject: "Subject", content: "<h1>Content</h1>", body: "<h2>Body</h2>")
+    2.times do
+      Message.create!(subject: "Subject", content: "<h1>Content</h1>", body: "<h2>Body</h2>")
+    end
+
+    message = assert_queries_count(3) do
+      # 3 queries:
+      # messages x 1
+      # action texts (content) x 1
+      # action texts (body) x 1
+      Message.with_all_rich_text.to_a.last
+    end
 
-    message = assert_queries_count(1) { Message.with_all_rich_text.last }
     assert_no_queries do
       assert_equal "Content", message.content.to_plain_text
       assert_equal "Body", message.body.to_plain_text