[lldb-dap] Destroy debugger when debug session terminates (llvm#156231)

# Patch

Currently, in Server Mode (i.e. `--connection`), all debuggers are
destroyed when the **lldb-dap process** terminates. This causes logging
and release of resources to be delayed. This can also cause congestion
if multiple debuggers have the same destroy callbacks, which will fight
for the same resources (e.g. web requests) at the same time.

Instead, the debuggers can be destroyed as early as when the **debug
session** terminates. This way, logging and release of release of
resources can happen as soon as possible. Congestion can also be
naturally reduced, because it's unlikely that all debug sessions will
terminate at the same time.

# Tests

See PR llvm#156231.

Author: royitaqi

lldb/tools/lldb-dap/DAP.cpp

@@ -1069,6 +1069,11 @@ llvm::Error DAP::Loop() {
     out.Stop();
     err.Stop();
     StopEventHandlers();
+
+    // Destroy the debugger when the session ends. This will trigger the
+    // debugger's destroy callbacks for earlier logging and clean-ups, rather
+    // than waiting for the termination of the lldb-dap process.
+    lldb::SBDebugger::Destroy(debugger);
   });
 
   while (true) {

lldb/tools/lldb-dap/EventHelper.cpp

@@ -230,15 +230,7 @@ llvm::Error SendThreadStoppedEvent(DAP &dap, bool on_entry) {
 
 // Send a "terminated" event to indicate the process is done being
 // debugged.
-void SendTerminatedEvent(DAP &dap) {
-  // Prevent races if the process exits while we're being asked to disconnect.
-  llvm::call_once(dap.terminated_event_flag, [&] {
-    dap.RunTerminateCommands();
-    // Send a "terminated" event
-    llvm::json::Object event(CreateTerminatedEventObject(dap.target));
-    dap.SendJSON(llvm::json::Value(std::move(event)));
-  });
-}
+void SendTerminatedEvent(DAP &dap) { dap.SendTerminatedEvent(); }
 
 // Grab any STDOUT and STDERR from the process and send it up to VS Code
 // via an "output" event to the "stdout" and "stderr" categories.