Vocabulary overview page (admin/structure/taxonomy_manager/voc) is not sorted by label [#3625035]

Problem/Motivation

MainController::listVocabularies(), which renders the vocabulary list at admin/structure/taxonomy_manager/voc, loads vocabularies with the following code, with no sorting applied at all.

$vocabularies = $this->entityTypeManager()->getStorage('taxonomy_vocabulary')->loadMultiple();
foreach ($vocabularies as $vocabulary) {
  // …
}

loadMultiple() for a config entity storage returns entities in the order the config storage lists them, which in practice is alphabetical by machine name (entity ID), not by the human-readable label. On a site with more than a handful of vocabularies whose machine names don't happen to match their labels' order, the list looks essentially random to an editor, even though it actually is sorted — just on a key nobody sees.

Steps to reproduce

Create (or use existing) vocabularies whose machine name doesn't sort the same way as their label, e.g. machine name references (label "Références") next to machine name object (label "Objet"): object sorts before references by machine name, but "Objet" sorts after "Références" alphabetically.
Go to admin/structure/taxonomy_manager/voc.
Observe the vocabularies are listed in machine-name order, not label order.

Proposed resolution

Sort $vocabularies by label before building the table. Note: a plain strnatcasecmp() on the raw label is not enough on its own for languages with accented characters (a byte-wise comparison sorts any accented letter after 'z', e.g. "Série" would sort after "Sujet d'image" instead of before it) — the attached patch folds common Latin accents to their base letter before comparing, since the intl/Collator extension can't be assumed to be available on every hosting environment.