[lldb] Emit signpost intervals for progress events (NFC)

Emit signpost intervals for progress events so that when users report an
operation takes a long time, we can see investigate the issue with
Instruments.

Author: JDevlieghere

lldb/source/Core/Progress.cpp

@@ -10,6 +10,7 @@
 
 #include "lldb/Core/Debugger.h"
 #include "lldb/Utility/StreamString.h"
+#include "llvm/Support/Signposts.h"
 
 #include <cstdint>
 #include <mutex>
@@ -20,6 +21,9 @@ using namespace lldb_private;
 
 std::atomic<uint64_t> Progress::g_id(0);
 
+// Instrument progress events with singposts when supported.
+static llvm::ManagedStatic<llvm::SignpostEmitter> g_progress_signposts;
+
 Progress::Progress(std::string title, std::string details,
                    std::optional<uint64_t> total,
                    lldb_private::Debugger *debugger)
@@ -39,9 +43,15 @@ Progress::Progress(std::string title, std::string details,
   // Report to the ProgressManager if that subsystem is enabled.
   if (ProgressManager::Enabled())
     ProgressManager::Instance().Increment(m_progress_data);
+
+  // Start signpost interval right before the meaningful work starts.
+  g_progress_signposts->startInterval(this, m_progress_data.title);
 }
 
 Progress::~Progress() {
+  // End signpost interval as soon as possible.
+  g_progress_signposts->endInterval(this, m_progress_data.title);
+
   // Make sure to always report progress completed when this object is
   // destructed so it indicates the progress dialog/activity should go away.
   std::lock_guard<std::mutex> guard(m_mutex);