Add call+fallback for streamJournalChanged to watchman

Summary:
# Context

SubscribeStreamTemporary is a function that allows users to recieve notifications whenever there is a change to the edenFS journal. Despite intended to be a temporary function, it's been named as such for about 6 years.

# This Diff
This diff replaces the call for watchman to subscribeStreamTemporary with a call for streamJournalChanged. It adds a fallback call for older versions without streamJournalChanged

Reviewed By: jdelliot

Differential Revision: D68240121

fbshipit-source-id: 0c3f9e98060bf80c1e0e78b06d8ac102a8a19060

watchman/watcher/eden.cpp

@@ -1068,8 +1068,19 @@ class EdenView final : public QueryableView {
       GetJournalPositionCallback& getJournalPositionCallback,
       std::chrono::milliseconds settleTimeout) {
     auto client = getEdenClient(thriftChannel_);
-    auto stream = client->sync_subscribeStreamTemporary(
-        std::string(root->root_path.data(), root->root_path.size()));
+    apache::thrift::ClientBufferedStream<::facebook::eden::JournalPosition>
+        stream;
+    try {
+      stream = client->sync_streamJournalChanged(
+          std::string(root->root_path.data(), root->root_path.size()));
+    } catch (const apache::thrift::TApplicationException& exc) {
+      log(DBG,
+          "running eden version does not have streamJournalChanged, falling back to subscribeStreamTemporary: ",
+          exc.what(),
+          "\n");
+      stream = client->sync_subscribeStreamTemporary(
+          std::string(root->root_path.data(), root->root_path.size()));
+    }
     return std::move(stream).subscribeExTry(
         &subscriberEventBase_,
         [&settleCallback,