Fix crash voting on a heading with a content block

When voting investment projects, the sidebar was rendered without the
`@heading_content_blocks` being set. That resulted in a 500 error when
the heading had content blocks.

By extracting the logic to a component, we make sure the heading content
blocks are properly set every time this code is rendered, no matter
which controller is rendering the view.

app/components/budgets/investments/content_blocks_component.html.erb

@@ -0,0 +1,5 @@
+<ul class="no-bullet categories">
+  <% content_blocks.each do |content_block| %>
+    <%= raw content_block.body %>
+  <% end %>
+</ul>

app/components/budgets/investments/content_blocks_component.rb

@@ -0,0 +1,17 @@
+class Budgets::Investments::ContentBlocksComponent < ApplicationComponent
+  attr_reader :heading
+
+  def initialize(heading)
+    @heading = heading
+  end
+
+  def render?
+    heading&.allow_custom_content && content_blocks.any?
+  end
+
+  private
+
+    def content_blocks
+      heading.content_blocks.where(locale: I18n.locale)
+    end
+end