Deprecate "KeyTemplate.getOutputPrefixType"

PiperOrigin-RevId: 548647821
diff --git a/java_src/src/main/java/com/google/crypto/tink/KeyTemplate.java b/java_src/src/main/java/com/google/crypto/tink/KeyTemplate.java
index 0d0f5dd..9663fc0 100644
--- a/java_src/src/main/java/com/google/crypto/tink/KeyTemplate.java
+++ b/java_src/src/main/java/com/google/crypto/tink/KeyTemplate.java
@@ -130,6 +130,13 @@
     return kt.getValue().toByteArray();
   }
 
+  /**
+   * @deprecated Instead, operate on the {@link Parameters} object obtained with {@link
+   *     #toParameters}. If you really need this value, you need to first use
+   *     TinkProtoParametersFormat to serialize this parameters object, then parse the result with
+   *     the Tink-internal proto class "KeyTemplate".
+   */
+  @Deprecated
   public OutputPrefixType getOutputPrefixType() {
     return fromProto(kt.getOutputPrefixType());
   }