log number of deleted inodes after GC completes

Summary:
## Log Number of Deleted Inodes After GC Completes
This diff adds logging for the number of deleted inodes after the Garbage Collector (GC) completes.

**Changes:**

* In `EdenServer.cpp`, the lambda function passed to `thenTry` now captures the `totalNumberOfInodesBeforeGC` variable, which is used to calculate the number of deleted inodes.
* In `LogEvent.h`, a new field `numOfDeletedInodes` is added to the `WorkingCopyGc` struct, along with a new constructor parameter to initialize it. The `populate` function is updated to include this new field.

**Purpose:**

This diff aims to provide additional logging information about the GC process, specifically the number of inodes deleted after completion. This can help with debugging and monitoring the performance of the GC.

Reviewed By: MichaelCuevas, jdelliot

Differential Revision: D75327069

fbshipit-source-id: 4d1b056e4e040a0e391120868565917a57ae5be2

Author: kavehahmadi60

eden/fs/service/EdenServer.cpp

@@ -2753,20 +2753,26 @@ ImmediateFuture<uint64_t> EdenServer::garbageCollectWorkingCopy(
       .thenTry([workingCopyRuntime,
                 structuredLogger = structuredLogger_,
                 mountPath,
-                inodeMap = mount.getInodeMap()](
+                inodeMap = mount.getInodeMap(),
+                totalNumberOfInodesBeforeGC](
                    folly::Try<uint64_t> numInvalidatedTry) {
         auto runtime =
             std::chrono::duration<double>{workingCopyRuntime.elapsed()};
 
         bool success = numInvalidatedTry.hasValue();
         int64_t numInvalidated =
             success ? folly::to_signed(numInvalidatedTry.value()) : 0;
-        structuredLogger->logEvent(
-            WorkingCopyGc{runtime.count(), numInvalidated, success});
         auto inodeCountsAfterGC = inodeMap->getInodeCounts();
         auto totalNumberOfInodesAfterGC = inodeCountsAfterGC.fileCount +
             inodeCountsAfterGC.treeCount +
             inodeCountsAfterGC.unloadedInodeCount;
+
+        structuredLogger->logEvent(WorkingCopyGc{
+            runtime.count(),
+            numInvalidated,
+            success,
+            static_cast<int64_t>(
+                (totalNumberOfInodesBeforeGC - totalNumberOfInodesAfterGC))});
         XLOGF(
             DBG1,
             "GC for: {}, completed in: {} seconds and invalidated {} inodes, total number of inodes {}",

eden/fs/telemetry/LogEvent.h

@@ -586,14 +586,23 @@ struct WorkingCopyGc : public EdenFSEvent {
   double duration = 0.0;
   int64_t numInvalidated = 0;
   bool success = false;
+  int64_t numOfDeletedInodes = 0;
 
-  WorkingCopyGc(double duration, int64_t numInvalidated, bool success)
-      : duration(duration), numInvalidated(numInvalidated), success(success) {}
+  WorkingCopyGc(
+      double duration,
+      int64_t numInvalidated,
+      bool success,
+      int64_t numOfDeletedInodes)
+      : duration(duration),
+        numInvalidated(numInvalidated),
+        success(success),
+        numOfDeletedInodes(numOfDeletedInodes) {}
 
   void populate(DynamicEvent& event) const override {
     event.addDouble("duration", duration);
     event.addInt("num_invalidated", numInvalidated);
     event.addBool("success", success);
+    event.addInt("num_deleted_inodes", numOfDeletedInodes);
   }
 
   const char* getType() const override {