Important: #79847 - Fluid bugs fixed and features added (Fluid 2.3.1)

Description

The Fluid engine dependency is raised to version 2.3.1 which fixes a few important bugs and adds a couple of features:

• Namespace declarations ({namespace foo=Bar\Baz\ViewHelpers} style) are now removed from output https://github.com/TYPO3/Fluid/pull/262
• The TemplatePaths object now accepts arrays for sanitizePath like the TYPO3 CMS adapter does. https://github.com/TYPO3/Fluid/pull/263
• Compiler is reset after each rendering - this fixes an issue where rendering the new HeaderAssets and FooterAssets sections would fail to attach the assets until the Fluid template had been compiled (first page hit after cache flush). https://github.com/TYPO3/Fluid/pull/269

And in the new features department, two new features are added:

• XML namespace extraction is brought into sync with TYPO3 CMS adapter https://github.com/TYPO3/Fluid/pull/264
• An escaping modifier pre-processor has been added https://github.com/TYPO3/Fluid/pull/266

This means two things:

1. For template developers this means you can use {escaping off} in a template to completely disable the escaping which is normally done - which can be particularly helpful in non-HTML templates.
2. For the TYPO3 core this means it becomes possible to drop two classes (Fluid overrides) completely from the source; namely the XmlnsNamespaceTemplatePreProcessor and LegacyNamespaceExpressionNode. Thus increasing the parsing efficiency of Fluid as it is integrated with TYPO3 CMS.