kvcoord: raise ambiguous errors on batches with commit

WIP: This intends to raise an error on a KV batch that has an ambiguous
error on one of its writes, and also has an `EndTxn` request in the
batch.

Part of: cockroachdb#103817

Release note (bug fix): TBD

pkg/kv/kvclient/kvcoord/dist_sender.go

@@ -2340,7 +2340,7 @@ func (ds *DistSender) sendToReplicas(
 			// evaluating twice, overwriting another unrelated write that fell
 			// in-between.
 			//
-			if withCommit && !grpcutil.RequestDidNotStart(err) {
+			if withCommit {
 				ambiguousError = err
 			}
 			log.VErrEventf(ctx, 2, "RPC error: %s", err)