Update SelectQuery interface to closely resemble core database API

I'm doing some cleanup on unsupported branches.
Please re-open this issue and update the version to 5.0.x-dev if this issue is still applicable to the latest release.

Hello, @aaronbauman
We are going to extend Drupal\salesforce\SelectQuery by adding simple functions. This will allow us to create chains like

$query
  ->fields(['field1', 'field2'])
  ->addCondition('status', 1)
  ->addOrder('DateCreated', 'DESC')
  ->limit(1);

Does it make sense to propose these functions for inclusion in Drupal\salesforce\SelectQuery? If not, can we safely use our derived class with these functions?

public function objectType($value) {
    $this->objectType = $value;
    return $this;
  }

  public function fields(array $fields) {
    $this->fields = $fields;
    return $this;
  }

  public function addField($field) {
    $this->fields[] = $field;
    return $this;
  }

  public function order(array $order) {
    $this->order = $order;
    return $this;
  }

  public function addOrder($field, $value = 'ASC') {
    $this->order[$field] = $value;
    return $this;
  }

  public function limit($value) {
    $this->limit = (int) $value;
    return $this;
  }

  public function offset($value) {
    $this->offset = (int) $value;
    return $this;
  }