DEV: Improve add_to_serializer include_* options (#21073)

- Move the old '`define_include_method`' arg to a `respect_plugin_enabled` kwarg
- Introduce an `include_condition` kwarg which can be passed a lambda with inclusion logic. Lambda will be run via `instance_exec` in the context of the serializer instance

This is backwards compatible - old-style invocations will trigger a deprecation message

Update chat and poll plugins to new pattern

plugins/poll/plugin.rb

@@ -195,7 +195,7 @@ after_initialize do
       end
   end
 
-  add_to_serializer(:post, :preloaded_polls, false) do
+  add_to_class(PostSerializer, :preloaded_polls) do
     @preloaded_polls ||=
       if @topic_view.present?
         @topic_view.polls[object.id]
@@ -204,15 +204,18 @@ after_initialize do
       end
   end
 
-  add_to_serializer(:post, :include_preloaded_polls?) { false }
-
-  add_to_serializer(:post, :polls, false) do
+  add_to_serializer(:post, :polls, include_condition: -> { preloaded_polls.present? }) do
     preloaded_polls.map { |p| PollSerializer.new(p, root: false, scope: self.scope) }
   end
 
-  add_to_serializer(:post, :include_polls?) { SiteSetting.poll_enabled && preloaded_polls.present? }
-
-  add_to_serializer(:post, :polls_votes, false) do
+  add_to_serializer(
+    :post,
+    :polls_votes,
+    include_condition: -> do
+      scope.user&.id.present? && preloaded_polls.present? &&
+        preloaded_polls.any? { |p| p.has_voted?(scope.user) }
+    end,
+  ) do
     preloaded_polls
       .map do |poll|
         user_poll_votes =
@@ -227,11 +230,6 @@ after_initialize do
       .to_h
   end
 
-  add_to_serializer(:post, :include_polls_votes?) do
-    SiteSetting.poll_enabled && scope.user&.id.present? && preloaded_polls.present? &&
-      preloaded_polls.any? { |p| p.has_voted?(scope.user) }
-  end
-
   register_search_advanced_filter(/in:polls/) do |posts, match|
     if SiteSetting.poll_enabled
       posts.joins(:polls)