Add structured data to download page

[jonoaldersonwp]

The download page (wordpress.org/download/ and rosetta variants) should include the following script.

Note that:

• URL/etc values should be localised where appropriate.
• Software versions should be maintained/correct.
• The description is taken from the page's meta description.
• The 'date modified' and version values should correspond with the latest release (i.e., the time that latest.zip was last updated).
• Google requires a operatingSystem property, which doesn't quite fit our context, so I've intentionally botched this into an array of vaguely-useful values. It'll do as-is, though feel free to refine+improve+extend.

<script type="application/ld+json">
[
    {
        "@context": "http://schema.org",
        "@type": [
            "SoftwareApplication",
            "Product"
        ],
        "name": "WordPress",
        "operatingSystem": ["Linux","Windows","Unix","Apache","NGINX"],
        "applicationCategory": "WebApplication",
        "url": "https://wordpress.org/download/",
        "description": "Download WordPress today, and get started on creating your website with one of the most powerful, popular, and customizable platforms in the world.",
        "softwareVersion": "5.3.2",
        "fileFormat": "application/zip",
        "downloadUrl": "https://wordpress.org/latest.zip",
        "dateModified": "2020-03-03T07:59:44+00:00",
        "offers": {
            "@type": "Offer",
            "url": "https://wordpress.org/download/",
            "price": "0.00",
            "priceCurrency": "USD",
            "seller": {
                "@type": "Organization",
                "name": "WordPress.org",
                "url": "https://wordpress.org"
            }
        }
    }
]
</script>

[dufresnesteven]

I've tested the block you provided with Google's structure data tool and got the following errors.

[dufresnesteven]

@jonoaldersonwp It appears to want 2 offers because we have 2 types listed. What do you suggest?

[jonoaldersonwp]

@dufresnesteven Their wording is poor.
Resolved with the addition of a "applicationCategory": "WebApplication" property/value pair.

[dufresnesteven]

TODO: I wasn't sure the best way to get the date modified. Anybody know how? Google Structured Data tool doesn't get upset without it, but i'm sure we should find a reliable way.

[dd32]

In 9689:

WordPress.org: Downloads: Add Structured Data tags to the download pages.

Props dufresnesteven for initial patch.
Fixes #5079.