Prepare to move changes since API from streaming to non-streaming

Summary:
# Context

We are introducing EdenFS notifications to support scalable and ergonomic file system notifications for EdenFS mounts.

# This Diff

Based on user feedback as well as discussions with former Watchman/EdenFS SWEs, we are planning to move from a streaming endpoint to a non-streaming endpoint. There are many reasons, but ergonomics and peformance (for this use case) are top reasons.

This diff moves some defintions from the streaming API to the non-streaming API.

# Next Steps

* Continue migrating the streaming interface to a non-streaming interface.
* Collapsing journal entries
* .t tests, Python integration tests, C++ unit tests

# Discussion Points

None

Differential Revision: D66026081

fbshipit-source-id: c7d1652f3a42d2854db5fba948706fe316376ef9

eden/fs/service/eden.thrift

@@ -1752,6 +1752,64 @@ union CheckoutProgressInfoResponse {
   2: CheckoutNotInProgress noProgress;
 }
 
+/*
+ * Structs/Unionts for changesSince API
+ */
+struct Added {
+  1: Dtype fileType;
+  3: PathString path;
+}
+
+struct Modified {
+  1: Dtype fileType;
+  3: PathString path;
+}
+
+struct Renamed {
+  1: Dtype fileType;
+  2: PathString from;
+  3: PathString to;
+}
+
+struct Replaced {
+  1: Dtype fileType;
+  2: PathString from;
+  3: PathString to;
+}
+
+struct Removed {
+  1: Dtype fileType;
+  3: PathString path;
+}
+
+union SmallChangeNotification {
+  1: Added added;
+  2: Modified modified;
+  3: Renamed renamed;
+  4: Replaced replaced;
+  5: Removed removed;
+}
+
+struct DirectoryRenamed {
+  1: PathString from;
+  2: PathString to;
+}
+
+struct CommitTransition {
+  1: ThriftRootId from;
+  2: ThriftRootId to;
+}
+
+union LargeChangeNotification {
+  1: DirectoryRenamed directoryRenamed;
+  2: CommitTransition commitTransition;
+}
+
+union ChangeNotification {
+  1: SmallChangeNotification smallChange;
+  2: LargeChangeNotification largeChange;
+}
+
 service EdenService extends fb303_core.BaseService {
   list<MountInfo> listMounts() throws (1: EdenError ex);
   void mount(1: MountArgument info) throws (1: EdenError ex);

eden/fs/service/streamingeden.thrift

@@ -62,61 +62,6 @@ const i64 FS_EVENT_READ = 1;
 const i64 FS_EVENT_WRITE = 2;
 const i64 FS_EVENT_OTHER = 4;
 
-struct Added {
-  1: eden.Dtype fileType;
-  3: eden.PathString path;
-}
-
-struct Modified {
-  1: eden.Dtype fileType;
-  3: eden.PathString path;
-}
-
-struct Renamed {
-  1: eden.Dtype fileType;
-  2: eden.PathString from;
-  3: eden.PathString to;
-}
-
-struct Replaced {
-  1: eden.Dtype fileType;
-  2: eden.PathString from;
-  3: eden.PathString to;
-}
-
-struct Removed {
-  1: eden.Dtype fileType;
-  3: eden.PathString path;
-}
-
-union SmallChangeNotification {
-  1: Added added;
-  2: Modified modified;
-  3: Renamed renamed;
-  4: Replaced replaced;
-  5: Removed removed;
-}
-
-struct DirectoryRenamed {
-  1: eden.PathString from;
-  2: eden.PathString to;
-}
-
-struct CommitTransition {
-  1: eden.ThriftRootId from;
-  2: eden.ThriftRootId to;
-}
-
-union LargeChangeNotification {
-  1: DirectoryRenamed directoryRenamed;
-  2: CommitTransition commitTransition;
-}
-
-union ChangeNotification {
-  1: SmallChangeNotification smallChange;
-  2: LargeChangeNotification largeChange;
-}
-
 /**
  * The value of a stream item.
  *
@@ -144,7 +89,7 @@ struct ChangesSinceResult {
  * since the notification clock provided.
  */
 struct ChangeNotificationResult {
-  1: ChangeNotification change;
+  1: eden.ChangeNotification change;
 }
 
 /**