Issue #3387988 by quietone, atul4drupal: Fix @return type, simple fixes

core/lib/Drupal/Core/Config/ImmutableConfig.php

.../Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php

core/lib/Drupal/Core/Menu/menu.api.php

core/lib/Drupal/Core/Render/theme.api.php

...rmalizer/Value/TemporaryArrayObjectThrowingExceptions.php

core/modules/locale/locale.compare.inc

core/modules/locale/src/PluralFormula.php

core/modules/rest/src/Routing/ResourceRoutes.php

core/phpstan-baseline.neon

core/tests/Drupal/KernelTests/Core/Entity/EntityTypeTest.php

...tests/Drupal/Tests/Core/TempStore/SharedTempStoreTest.php