[Java Client] Let producer reconnect for state RegisteringSchema (apa…

…che#12781)

Motivation
In the Java Client, if a producer is in the RegisteringSchema state, it is a valid state for it to reconnect. Fix the ConnectionHandler to align with this behavior.

Modifications
Update the isValidStateForReconnection method to return true for state RegisteringSchema.
Verifying this change
This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:
This update does not contain breaking changes.

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConnectionHandler.java

@@ -156,6 +156,7 @@ private boolean isValidStateForReconnection() {
         switch (state) {
             case Uninitialized:
             case Connecting:
+            case RegisteringSchema:
             case Ready:
                 // Ok
                 return true;