[BUGFIX] Reduce amount of Cache::set() calls in AssetService

With TYPO3 v13, AssetService calls FrontendInterface::set() four times
in AssetService::getTypoScript() for a single AssetService::buildAll()
invocation. The cache usage was introduced in e84af96 ("[BUGFIX] Handle
new TS-not-set limitation on v13 (#1928)"), as TYPO3 v13 no longer fully
sets up TypoScript when serving fully-cached pages.

The four callers of AssetService::getTypoScript() are:

- AssetService::getSettings()
- AssetService::writeCachedMergedFileAndReturnTag()
- AssetService::getFileIntegrity()
- AssetService::generateTagForAssetType()

Reducing the number of FrontendInterface::set() calls reduces the amount
of database deadlock errors that occur if the Typo3DatabaseBackend is
used for the "vhs_main" cache and many concurrent requests hit the same
TYPO3 page that contains at least one uncached content element. But it
doesn't solve them completely; e.q. They still occur but less frequent.
This issue is tracked in the upstream TYPO3 bug tracker as #106593 [1].
A reproduction example is available on GitHub [2].

[1]: https://forge.typo3.org/issues/106593
[2]: https://github.com/adamkoppede/reproduce-deadlock-with-fluidtypo3-vhs-7-1

Classes/Service/AssetService.php

@@ -49,7 +49,7 @@ class AssetService implements SingletonInterface
     protected $cacheManager;
 
     protected static bool $typoScriptAssetsBuilt = false;
-    protected static ?array $settingsCache = null;
+    protected static ?array $typoScriptCache = null;
     protected static array $cachedDependencies = [];
     protected static bool $cacheCleared = false;
 
@@ -145,15 +145,15 @@ public function isAlreadyDefined(string $assetName): bool
      */
     public function getSettings(): array
     {
-        if (null === static::$settingsCache) {
-            static::$settingsCache = $this->getTypoScript()['settings'] ?? [];
-        }
-        $settings = (array) static::$settingsCache;
-        return $settings;
+        return $this->getTypoScript()['settings'] ?? [];
     }
 
     protected function getTypoScript(): array
     {
+        if (static::$typoScriptCache !== null) {
+            return static::$typoScriptCache;
+        }
+
         $cache = $this->cacheManager->getCache('vhs_main');
         $pageUid = $this->readPageUidFromContext();
         $cacheId = 'vhs_asset_ts_' . $pageUid;
@@ -192,6 +192,7 @@ protected function getTypoScript(): array
             $this->cacheManager->flushCachesByTag($cacheTag);
         }
 
+        static::$typoScriptCache = $typoScript;
         return $typoScript;
     }