Feature: #104114 - Command to generate Fluid schema files

See forge#104114

Description

With Fluid Standalone 2.12, a new implementation of the XSD schema generator has been introduced, which was previously a separate composer package. These XSD files allow IDEs to provide autocompletion for ViewHelper arguments in Fluid templates, provided that they are included in the template by using the xmlns syntax:

<html
    xmlns:f="http://typo3.org/ns/TYPO3/CMS/Fluid/ViewHelpers"
    xmlns:my="http://typo3.org/ns/Vendor/MyPackage/ViewHelpers"
    data-namespace-typo3-fluid="true"
>
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A new CLI command has been defined to apply Fluid's new schema generator to TYPO3's Fluid integration. New Fluid APIs are used to find all ViewHelpers that exist in the current project (based on the composer autoloader). Then, TYPO3's configuration is checked for any merged Fluid namespaces (like f:, which consists of both Fluid Standalone and EXT:fluid ViewHelpers which in some cases override each other).

After that consolidation, *.xsd files are created in var/transient/ using another API from Fluid Standalone. These files which will automatically get picked up by supporting IDEs (like PhpStorm) to provide autocompletion in template files.

Impact

To get autocompletion for all available ViewHelpers in supporting IDEs, the following CLI command can be executed in local development environments:

::
vendor/bin/typo3 fluid:schema:generate