Added generics to Context

[chack1172]

This change will allow laravel-ide-helper to pass generics of class template to methods DocBlock using Context class.

Example class:

/**
 * @template TModel of \Illuminate\Database\Eloquent\Model
 */
class Builder
{
    /**
     * Get the first record matching the attributes or instantiate it.
     *
     * @param  array  $attributes
     * @param  array  $values
     * @return TModel
     */
    public function firstOrNew(array $attributes = [], array $values = [])
    {}
}

In this way:

$classDocBlock = new DocBlock($classDocBlockText);
$methodDocBlock = new DocBlock($methodDocBlockText, new Context($namespace, $classAliases, '', $classDocBlock->getGenerics()))