Allow providing computed method for To header

[DaAwesomeP]

Hello,

I am trying to do the following so that the mail header To field contains a user's name as well as email address.

class ApplicationDeviseMailer < Devise::Mailer
  default to: -> { computed_to }

  private

  def computed_to
    ApplicationMailer.email_address_with_name(resource.email, resource.name)
  end
end

However, there is not an option to transform the To field (only From and Reply-To):

devise/lib/devise/mailers/helpers.rb

Lines 31 to 48 in fec67f9

	def headers_for(action, opts)
	headers = {
	subject: subject_for(action),
	to: resource.email,
	from: mailer_sender(devise_mapping),
	reply_to: mailer_sender(devise_mapping),
	template_path: template_paths,
	template_name: action
	}
	# Give priority to the mailer's default if they exists.
	headers.delete(:from) if default_params[:from]
	headers.delete(:reply_to) if default_params[:reply_to]
	headers.merge!(opts)
	@email = headers[:to]
	headers
	end