Fix the coding Standard issues in Geocoder module.

Solved the following errors and warnings:

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1. t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
2. Description for the @return value is missing.
3. The class short comment should describe what the class does and not the class name.
4. #description values usually have to run through t() for translation.
5. The array declaration extends to column 112 (the limit is 80).