Support additional search page plugins.

Problem/Motivation

Right now, search_current_language only supports the core search.node_search plugin.

There are contrib modules who also provide search page plugins.
- https://drupal.org/project/search_exclude

Saw an issue on the search_exclude project #3343993: Not compatible with search_current_language module

Steps to reproduce

Install search_exclude and configure as described on the project page.
Install search_current_language module and set multiple languages.
Install devel_generate module and create a lot of demo content of varying languages.
Run cron to ensure everything is indexed.
Attempt to use your search exclude search page, and see that your searches are not filtered by the current language.

Proposed resolution

Add configuration for enabling on any search page plugin. (Or just support all automatically)

Remaining tasks

Merge request

User interface changes

Search page plugins other than core now utilize this module's functionality.

API changes

N/A

Data model changes

Depends on implementation.