DEV: extract inline js when baking theme fields (#6447)

* extract inline js when baking theme fields
* destroy javascript cache when destroying theme fields

This work is needed to support CSP work

app/models/javascript_cache.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+class JavascriptCache < ActiveRecord::Base
+  belongs_to :theme_field
+
+  validate :content_cannot_be_nil
+
+  before_save :update_digest
+
+  def url
+    "#{GlobalSetting.cdn_url}#{GlobalSetting.relative_url_root}/javascripts/#{digest}.js"
+  end
+
+  private
+
+  def update_digest
+    self.digest = Digest::SHA1.hexdigest(content) if content_changed?
+  end
+
+  def content_cannot_be_nil
+    errors.add(:content, :empty) if content.nil?
+  end
+end
+
+# == Schema Information
+#
+# Table name: javascript_caches
+#
+#  id             :bigint(8)        not null, primary key
+#  theme_field_id :bigint(8)        not null
+#  digest         :string
+#  content        :text             not null
+#  created_at     :datetime         not null
+#  updated_at     :datetime         not null
+#
+# Indexes
+#
+#  index_javascript_caches_on_digest          (digest)
+#  index_javascript_caches_on_theme_field_id  (theme_field_id)
+#