hreflang sets should always include the current value

[jonoaldersonwp]

Our hreflang implementation should be modified to ensure that the requested 'version' of a page is always present in the set; regardless of its translation status.

E.g:

• ​https://nn.wordpress.org/plugins/contact-form-7/ should have a nn value.
• ​https://en-za.wordpress.org/plugins/akismet/ should have a en-za value.

[dd32]

In 10668:

Plugin Directory: Always include the current locale site in the list of hreflang tags.

Fixes #5614.