[SearchBundle] Add the locale to the request context when populating the search index

[jockri]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Fixed tickets

When the search index gets populated, their was no _locale parameter in the RenderContext because the command is executed from the command line. The _locale parameter is in the context for browser requests, so it is also needed when populating the search index.

Example use case:
When you have this peace of code in twig, it works for browser requests, but not when populating the search index.

<a href="{{ path('_slug', { url: nodeTranslation.url }) }}">click here</a>

[krispypen]

@roderik 👍