8331346: Update PreviewFeature of STREAM_GATHERERS to JEP-473

Reviewed-by: pminborg, alanb

Author: Viktor Klang

src/java.base/share/classes/jdk/internal/javac/PreviewFeature.java

@@ -79,7 +79,7 @@ public enum Feature {
         STRUCTURED_CONCURRENCY,
         @JEP(number=466, title="ClassFile API", status="Second Preview")
         CLASSFILE_API,
-        @JEP(number=461, title="Stream Gatherers", status="Preview")
+        @JEP(number=473, title="Stream Gatherers", status="Second Preview")
         STREAM_GATHERERS,
         LANGUAGE_MODEL,
         /**