fix: do not serialize unnecessary fields (#1426)

Do not serialize java.util.regex.Pattern and executor fields in client side statement. This caused an issue with Java 16 compilation, where an IllegalAccessException is thrown during JSON serialization of such fields.

Author: thiagotnunes

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ClientSideStatementImpl.java

@@ -131,10 +131,10 @@ public String getMessage() {
  private ClientSideSetStatementImpl setStatement;
 
  /** The compiled regex pattern for recognizing this statement. */
- private Pattern pattern;
+ private transient Pattern pattern;
 
  /** A reference to the executor that should be used. */
- private ClientSideStatementExecutor executor;
+ private transient ClientSideStatementExecutor executor;
 
  /**
  * Compiles this {@link ClientSideStatementImpl}. Throws a {@link CompileException} if the