Feature: #109187 - Add integrity property to CSS includes 

Description 

The TypoScript properties includeCSS and includeCSSLibs now support the integrity property for Subresource Integrity (SRI) checking, bringing CSS includes to parity with existing SRI support in includeJS, includeJSFooter, includeJSLibs, and includeJSFooterlibs.

The crossorigin property is also supported. When integrity is set without an explicit crossorigin value for URI resources (for example, external URLs), crossorigin="anonymous" is automatically added, which is required for SRI validation to work cross-origin.

The integrity attribute has not yet been added to inline styles ( inline = 1), as SRI only applies to external resources.

The PageRenderer::addCssFile() and PageRenderer::addCssLibrary() methods have gained two new parameters, $integrity and $crossorigin.

Impact 

It is now possible to add SRI integrity hashes to CSS files included via TypoScript:

page.includeCSS {
    main = https://cdn.example.com/styles/main.css
    main.integrity = sha384-abc123==
    # crossorigin is auto-set to "anonymous" when integrity is given
}

page.includeCSSLibs {
    vendor = https://cdn.example.com/vendor.css
    vendor.integrity = sha384-xyz789==
    vendor.crossorigin = anonymous
}

This results in the following HTML output:

<link rel="stylesheet" href="https://cdn.example.com/styles/main.css" media="all" integrity="sha384-abc123==" crossorigin="anonymous">