Feature: #94501 - FAL support for FlexFormProcessor

See forge#94501

Description

The FlexFormProcessor is now able to resolve FAL references by its own.

Each FlexForm field, which should be resolved, needs a reference definition to the foreign_match_fields. This reference is later used in the FilesProcessor to resolve the correct FAL resource.

Example of an advanced TypoScript configuration, which processes the field my_flexform_field, resolves its FAL references and assigns the array to the myOutputVariable variable:

10 = TYPO3\CMS\Frontend\DataProcessing\FlexFormProcessor
10 {
  fieldName = my_flexform_field
  references {
    my_flex_form_group.my_flex_form_field = my_field_reference
  }
  as = myOutputVariable
}
<my_flex_form_group.my_flex_form_field>
   <label>LLL:EXT:sitepackage/Resources/Private/Language/locallang_be.xlf:my_flex_form_field</label>
   <config>
      <type>file</type>
      <maxitems>9</maxitems>
      <foreign_selector_fieldTcaOverride>
         <config>
            <appearance>
               <elementBrowserType>file</elementBrowserType>
               <elementBrowserAllowed>gif,jpg,jpeg,png,svg</elementBrowserAllowed>
            </appearance>
         </config>
      </foreign_selector_fieldTcaOverride>
      <foreign_types type="array">
         <numIndex index="0">
            <showitem>--palette--;LLL:EXT:lang/locallang_tca.xlf:sys_file_reference.imageoverlayPalette;imageoverlayPalette,--palette--;;filePalette</showitem>
         </numIndex>
         <numIndex index="2">
            <showitem>--palette--;LLL:EXT:lang/locallang_tca.xlf:sys_file_reference.imageoverlayPalette;imageoverlayPalette,--palette--;;filePalette</showitem>
         </numIndex>
      </foreign_types>
      <appearance type="array">
         <headerThumbnail>
            <height>64</height>
            <width>64</width>
         </headerThumbnail>
         <enabledControls>
            <info>1</info>
            <dragdrop>0</dragdrop>
            <sort>1</sort>
            <hide>0</hide>
            <delete>1</delete>
            <localize>1</localize>
         </enabledControls>
         <createNewRelationLinkTitle>LLL:EXT:frontend/Resources/Private/Language/locallang_ttc.xlf:images.addFileReference</createNewRelationLinkTitle>
      </appearance>
      <behaviour>
         <localizationMode>select</localizationMode>
         <localizeChildrenAtParentLocalization>1</localizeChildrenAtParentLocalization>
      </behaviour>
      <overrideChildTca>
         <types type="array">
            <numIndex index="2">
               <showitem>--palette--;LLL:EXT:lang/locallang_tca.xlf:sys_file_reference.imageoverlayPalette;imageoverlayPalette,--palette--;;filePalette</showitem>
            </numIndex>
         </types>
      </overrideChildTca>
      <allowed>jpg,png,svg,jpeg,gif</allowed>
   </config>
</my_flex_form_group.my_flex_form_field>

Impact

FAL references within a FlexForm can now be resolved for the direct usage in Fluid templates. This makes resolving the file references by using additional data processors obsolete.