ThemeRegistry is empty after Registry::destruct(), so later renders report "Theme hook X not found"

Problem/Motivation

#3486503 added $this->reset() to CacheCollector::destruct(). Drupal\Core\Utility\ThemeRegistry extends CacheCollector, and Registry::destruct() destructs every runtime registry but keeps returning the same objects from getRuntime(). After the reset their storage is empty, and ThemeRegistry::has() and get() read it without reloading.

As a result, anything rendered in the same process after theme.registry is destructed gets "Theme hook X not found" (field, links, time, ...) and the renderer outputs bare text. We hit it with Search API index_directly during drush cron: search_api.post_request_indexing is destructed after theme.registry and renders the entities saved during cron, so the indexed HTML has no templates. It only happens when the runtime registry was already used earlier in the same process. Seen on 11.4.6 and 11.4.8.

Steps to reproduce

$registry = \Drupal::service('theme.registry');
$registry->getRuntime()->has('container');   // TRUE
$registry->destruct();
$registry->getRuntime()->has('container');   // FALSE

Proposed resolution

In Registry::destruct(), empty ry after destructing the collectors, so
a later getRuntime() builds a fhe cache again.

Remaining tasks

Review.

User interface changes

None.

API changes

None.

Data model changes

None.