include compaction cursors in VersionEdit debug string (#10288)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/10288

Test Plan:
try it out -

```
$ ldb manifest_dump --db=/dev/shm/rocksdb.0uWV/rocksdb_crashtest_whitebox/ --hex --verbose | grep CompactCursor | head -3
  CompactCursor: 1 '00000000000011D9000000000000012B0000000000000266' seq:0, type:1
  CompactCursor: 1 '0000000000001F35000000000000012B0000000000000022' seq:0, type:1
  CompactCursor: 2 '00000000000011D9000000000000012B0000000000000266' seq:0, type:1
```

Reviewed By: littlepig2013

Differential Revision: D37557177

Pulled By: ajkr

fbshipit-source-id: 7b76b857d9e7a9f3d53398a61bb1d4b78873b91e

db/version_edit.cc

@@ -799,6 +799,12 @@ std::string VersionEdit::DebugString(bool hex_key) const {
     r.append("\n  LastSeq: ");
     AppendNumberTo(&r, last_sequence_);
   }
+  for (const auto& level_and_compact_cursor : compact_cursors_) {
+    r.append("\n  CompactCursor: ");
+    AppendNumberTo(&r, level_and_compact_cursor.first);
+    r.append(" ");
+    r.append(level_and_compact_cursor.second.DebugString(hex_key));
+  }
   for (const auto& deleted_file : deleted_files_) {
     r.append("\n  DeleteFile: ");
     AppendNumberTo(&r, deleted_file.first);