Update WordPress.org Openverse theme to pass i18n/L10n info to the iframe

[dhruvkb]

The GitHub PR (​https://github.com/WordPress/wordpress.org/pull/39) adds styling to ensure that the iframe on site ​https://wordpress.org/openverse receives i18n data from the parent window (when it asks for it).

Fixes WordPress/openverse-frontend#189

Closes https://meta.trac.wordpress.org/ticket/5892

---

This PR adds functionality for the Openverse frontend loaded in the iframe to ask the parent window information about the locale.

iframe —(localeGet event)→ parent window
iframe ←(localeSet event)— parent window

## Description

The localeSet message contains the following data:
{{{json
{

"type": "localeSet",
"value": {

"dir": "",
"lang": "en-US",
"locale": "en_US"

}

}
}}}

| Key | Interpretation |

|

| dir | Value of parent HTML dir attribute |
| lang | Value of parent HTML lang attribute |
| locale | Value of WordPress get_locale() function |

[dd32]

In 11217:

Openverse: Update the theme to pass the locale.

Fixes #5892.
Closes ​https://github.com/WordPress/wordpress.org/pull/39