Further improvements to plugin page schema

[jonoaldersonwp]

On plugin pages like ​https://en-gb.wordpress.org/plugins/wordpress-seo/, we should make further improvements to the schema.org markup to take advantage of rich(er) search engine results.

Specifically:

• Alter the @type property to ["SoftwareApplication","Product"].

• Add an operatingSystem property, with a value of WordPress.

• Alter the value of applicationCategory to Plugin.

• Add an image property, where the value is an array containing the (largest version of) the banner image, and the (largest version of) the plugin icon. E.g., ["https://ps.w.org/wordpress-seo/assets/banner-1544x500.png?rev=1843435", "https://ps.w.org/wordpress-seo/assets/icon-256x256.png?rev=1834347"].
  • If either image is not present/set, omit it from the array. If neither are present/set, don't set the image property at all.

• Add a url property to the offer (the local canonical URL of the plugin)

[jonoaldersonwp]

#5009 was marked as a duplicate.

[dd32]

In 9473:

Plugin Directory: Schema: Enhance the plugins schema to provice richer data.

Props jonoaldersonwp.
Fixes #5010.

[dd32]

Deployed, here's the new set of schema warnings:
​https://search.google.com/structured-data/testing-tool/u/0/#url=https%3A%2F%2Fen-au.wordpress.org%2Fplugins%2Fwordpress-seo%2F

offers.availability	The availability field is recommended. Please provide a value if available.
offers.priceValidUntil	The priceValidUntil field is recommended. Please provide a value if available.
brand	The brand field is recommended. Please provide a value if available.
review	The review field is recommended. Please provide a value if available.
sku	 The sku field is recommended. Please provide a value if available.
{identifier} This product is missing a global identifier (e.g. isbn, mpn or gtin8). Please see documentation for valid identifiers.

Most of these look like they're the result of adding the Product type.

[jonoaldersonwp]

No problem, they're all optional fields. This is super, thanks!

[dd32]

In 9699:

Plugin Directory: Avoid a PHP Notice in [9473].

See #5010.