Add IOActivityToString helper method (#13440)

Summary:
I have a place I want to use this helper method inside the Sally codebase. I have this functionality in my Sally diff right now, but I think it is generic enough to warrant putting alongside `Env::PriorityToString`.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/13440

Test Plan: Just the compiler and CI checks are sufficient IMO.

Reviewed By: hx235

Differential Revision: D70664597

Pulled By: archang19

fbshipit-source-id: 341de6c6e311a3f421ad093c2c216e5caa5034dd

env/env.cc

@@ -732,6 +732,37 @@ std::string Env::PriorityToString(Env::Priority priority) {
   return "Invalid";
 }
 
+std::string Env::IOActivityToString(IOActivity activity) {
+  switch (activity) {
+    case Env::IOActivity::kFlush:
+      return "Flush";
+    case Env::IOActivity::kCompaction:
+      return "Compaction";
+    case Env::IOActivity::kDBOpen:
+      return "DBOpen";
+    case Env::IOActivity::kGet:
+      return "Get";
+    case Env::IOActivity::kMultiGet:
+      return "MultiGet";
+    case Env::IOActivity::kDBIterator:
+      return "DBIterator";
+    case Env::IOActivity::kVerifyDBChecksum:
+      return "VerifyDBChecksum";
+    case Env::IOActivity::kVerifyFileChecksums:
+      return "VerifyFileChecksums";
+    case Env::IOActivity::kGetEntity:
+      return "GetEntity";
+    case Env::IOActivity::kMultiGetEntity:
+      return "MultiGetEntity";
+    case Env::IOActivity::kReadManifest:
+      return "ReadManifest";
+    case Env::IOActivity::kUnknown:
+      return "Unknown";
+  };
+  assert(false);
+  return "Invalid";
+}
+
 uint64_t Env::GetThreadID() const {
   std::hash<std::thread::id> hasher;
   return hasher(std::this_thread::get_id());

include/rocksdb/env.h

@@ -459,6 +459,8 @@ class Env : public Customizable {
     kUnknown,  // Keep last for easy array of non-unknowns
   };
 
+  static std::string IOActivityToString(IOActivity activity);
+
   // Arrange to run "(*function)(arg)" once in a background thread, in
   // the thread pool specified by pri. By default, jobs go to the 'LOW'
   // priority thread pool.