Modify locale handling to inspect request parameters

Description

The default behavior of WordPressComRestApi appends a locale parameter to requests. To do so, it inspects & modifies the path of a given request if needed.

If a caller were to specify locale in the request parameters, however, the specified value is not properly de-duplicated. For example, composing a GET request with the default behavior enabled, passing locale : foo in the request parameters evinces a request with the following URL : https://public-api.wordpress.com/wpcom/v2/<path>?locale=en&locale=foo.

Potential Solution

The client should inspect the parameters associated with the request, and de-duplicate those if necessary. It might be worth using URLComponents for this purpose.