SqlContentEntityStorage no longer update entities with certain (id) fields

Problem/Motivation

SqlContentEntityStorage::doSaveFieldItems() now assumes that entity id can be accessed via $entity->get($this->idKey)->value when updating entities. However this is not always the case.

Relevant diff from #2342699: SqlContentEntityStorage tries to update identity/serial values by default:

diff --git a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php
index 150a18d64b..7edc4f6307 100644
--- a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php
+++ b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php
@@ -824,10 +824,13 @@ protected function doSaveFieldItems(ContentEntityInterface $entity, array $names
       if ($update) {
         $default_revision = $entity->isDefaultRevision();
         if ($default_revision) {
+          // Remove the ID from the record to enable updates on SQL variants
+          // that prevent updating serial columns, for example, mssql.
+          unset($record->{$this->idKey});
           $this->database
             ->update($this->baseTable)
             ->fields((array) $record)
-            ->condition($this->idKey, $record->{$this->idKey})
+            ->condition($this->idKey, $entity->get($this->idKey)->value)
             ->execute();
         }

Proposed resolution

Remaining tasks

User interface changes

API changes