[SPARK-45541][CORE] Add SSLFactory

### What changes were proposed in this pull request?

As titled - add a factory which supports creating SSL engines, and a corresponding builder for it. This will be used in a follow up PR by the `TransportContext` and related files to add SSL support.

### Why are the changes needed?

We need a mechanism to initialize the appropriate SSL implementation with the configured settings (such as protocol, ciphers, etc) for RPC SSL support.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

existing tests. This will be more thoroughly tested in a follow up PR which adds callsites to it. It has been integration tested as part of #42685

### Was this patch authored or co-authored using generative AI tooling?

No

Closes #43386 from hasnain-db/spark-tls-factory.

Authored-by: Hasnain Lakhani <hasnain.lakhani@databricks.com>
Signed-off-by: Mridul Muralidharan <mridul<at>gmail.com>

Author: hasnain-db

common/network-common/src/main/java/org/apache/spark/network/protocol/SslMessageEncoder.java

@@ -36,7 +36,7 @@
 @ChannelHandler.Sharable
 public final class SslMessageEncoder extends MessageToMessageEncoder<Message> {
 
-  private final Logger logger = LoggerFactory.getLogger(SslMessageEncoder.class);
+  private static final Logger logger = LoggerFactory.getLogger(SslMessageEncoder.class);
 
   private SslMessageEncoder() {}
 

common/network-common/src/main/java/org/apache/spark/network/ssl/ReloadingX509TrustManager.java

@@ -46,7 +46,7 @@
 public final class ReloadingX509TrustManager
         implements X509TrustManager, Runnable {
 
-  private final Logger logger = LoggerFactory.getLogger(ReloadingX509TrustManager.class);
+  private static final Logger logger = LoggerFactory.getLogger(ReloadingX509TrustManager.class);
 
   private final String type;
   private final File file;
@@ -180,7 +180,8 @@ X509TrustManager loadTrustManager()
     canonicalPath = latestCanonicalFile.getPath();
     lastLoaded = latestCanonicalFile.lastModified();
     try (FileInputStream in = new FileInputStream(latestCanonicalFile)) {
-      ks.load(in, password.toCharArray());
+      char[] passwordCharacters = password != null? password.toCharArray() : null;
+      ks.load(in, passwordCharacters);
       logger.debug("Loaded truststore '" + file + "'");
     }