Helper function to get renderable region for Drupal 8

functions.php

<?php
// Example usage: $build = blocks_get_blocks_by_region('sidebar_first');

function blocks_get_blocks_by_region($region_name) {
  $build = [];

  $blocks = entity_load_multiple_by_properties('block', ['theme' => $GLOBALS['theme'], 'region' => $region_name]);
  uasort($blocks, 'Drupal\block\Entity\Block::sort');

  foreach ($blocks as $key => $block) {
    if ($block->access('view)) {
      $build[$key] = entity_view($block, 'block');
    }
  }

  return $build;
}