Do not create blob temp folder for ephemeral sessions

https://bugs.webkit.org/show_bug.cgi?id=257950
rdar://110545873

Reviewed by Sihui Liu.

We are creating a temp folder for blobs to use mapped memory to store blobs, as a way to limit networking process jetsams.
This creation was not dependent on session being ephemeral or not.
We are now skipping the creation of this temp folder for ephemeral sessions.
This will trigger use of regular memory for storing blobs, which may increase networking process jetsams.

* Source/WebKit/NetworkProcess/cocoa/NetworkSessionCocoa.mm:
(WebKit::NetworkSessionCocoa::NetworkSessionCocoa):

Canonical link: https://commits.webkit.org/265127@main

Source/WebKit/NetworkProcess/cocoa/NetworkSessionCocoa.mm

@@ -1403,7 +1403,8 @@ static void activateSessionCleanup(NetworkSessionCocoa& session, const NetworkSe
 
     NSURLSessionConfiguration *configuration = configurationForSessionID(m_sessionID, isParentProcessAFullWebBrowser(networkProcess));
 
-    m_blobRegistry.setFileDirectory(FileSystem::createTemporaryDirectory(@"BlobRegistryFiles"));
+    if (!m_sessionID.isEphemeral())
+        m_blobRegistry.setFileDirectory(FileSystem::createTemporaryDirectory(@"BlobRegistryFiles"));
 
     if (!!parameters.hstsStorageDirectory && !m_sessionID.isEphemeral()) {
         SandboxExtension::consumePermanently(parameters.hstsStorageDirectoryExtensionHandle);