fix: makes exceptions public so others can import and handle them

oauth2_http/java/com/google/auth/oauth2/CredentialFormatException.java

@@ -34,7 +34,7 @@
 import java.io.IOException;
 
 /** Indicates that the provided credential does not adhere to the required format. */
-class CredentialFormatException extends IOException {
+public class CredentialFormatException extends IOException {
   CredentialFormatException(String message, Throwable cause) {
     super(message, cause);
   }

oauth2_http/java/com/google/auth/oauth2/GoogleAuthException.java

@@ -39,7 +39,7 @@
  * Base class for the standard Auth error response. It extends a default exception while keeping
  * Json response format
  */
-class GoogleAuthException extends IOException implements Retryable {
+public class GoogleAuthException extends IOException implements Retryable {
 
   private final boolean isRetryable;
   private final int retryCount;

oauth2_http/java/com/google/auth/oauth2/OAuthException.java

@@ -39,7 +39,7 @@
  * Encapsulates the standard OAuth error response. See
  * https://tools.ietf.org/html/rfc6749#section-5.2.
  */
-class OAuthException extends GoogleAuthException {
+public class OAuthException extends GoogleAuthException {
 
   private final String errorCode;
   @Nullable private final String errorDescription;

oauth2_http/java/com/google/auth/oauth2/PluggableAuthException.java

@@ -34,7 +34,7 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 /** Encapsulates the error response's for 3rd party executables defined by the executable spec. */
-class PluggableAuthException extends OAuthException {
+public class PluggableAuthException extends OAuthException {
 
   PluggableAuthException(String errorCode, String errorDescription) {
     super(errorCode, checkNotNull(errorDescription), /* errorUri=*/ null);