filerepo: clean up remote description cache keys

Hash the file name portion and make the string constant portions
more relevant to what the keys are actually used for (e.g. there
is no URL parameter in the key)

Bug: T198279
Change-Id: Idf6f97db26f5be291cdd3a50a91346677fe9c3e6

includes/filerepo/file/File.php

@@ -2068,9 +2068,8 @@ abstract class File implements IDBAccessObject {
 			$cache = MediaWikiServices::getInstance()->getMainWANObjectCache();
 			$key = $this->repo->getLocalCacheKey(
 				'RemoteFileDescription',
-				'url',
 				$lang->getCode(),
-				$this->getName()
+				md5( $this->getName() )
 			);
 
 			return $cache->getWithSetCallback(

includes/filerepo/file/ForeignDBFile.php

@@ -155,10 +155,9 @@ class ForeignDBFile extends LocalFile {
 
 		return $cache->getWithSetCallback(
 			$this->repo->getLocalCacheKey(
-				'RemoteFileDescription',
-				'url',
+				'ForeignFileDescription',
 				$lang->getCode(),
-				$this->getName(),
+				md5( $this->getName() ),
 				$touched
 			),
 			$this->repo->descriptionCacheExpiry ?: $cache::TTL_UNCACHEABLE,