Feature: #90728 - Add FluidEmail option to EXT:form EmailFinisher
See forge#90728
Description
After the introduction of FluidEmail in v10 the option to send mails in a standardized way is now also added to the EmailFinisher of the system extension EXT:from.
To use FluidEmail a new option use is added to both the EmailToReceiver
and EmailToSender finisher. It defaults to 
        FALSE so extension authors are
able to smoothly test and upgrade their forms. Furthermore a new option title
is available which can be used to add an E-Mail title to the default FluidEmail
template. This option is capable of rendering form element variables using the
known bracket syntax and can be overwritten in the FlexForm configuration of the
form plugin.
To customize the templates beeing used following options can be set:
template: The template name (for both HTML and plaintext) without the extensionName template: The paths to the templatesRoot Paths partial: The paths to the partialsRoot Paths layout: The paths to the layoutsRoot Paths 
For FluidEmail, the field template is not evaluated anymore.
A finisher configuration could look like this:
identifier: contact
type: Form
prototypeName: standard
finishers:
-
   identifier: EmailToSender
   options:
      subject: 'Your Message: {message}'
      title: 'Hello {name}, your confirmation'
      templateName: ContactForm
      templateRootPaths:
         100: 'EXT:sitepackage/Resources/Private/Templates/Email/'
      partialRootPaths:
         100: 'EXT:sitepackage/Resources/Private/Partials/Email/'
      addHtmlPart: true
      useFluidEmail: true
    Please note that the old template name syntax {@format}. does not work for
FluidEmail as each format needs a different template with the corresponing file
extension. In the example above the following files must exist in the specified
template path:
ContactForm. html ContactForm. txt 
Impact
It's now possible to use FluidEmail for sending mails in EXT:form.