[lldb-dap] Use heterogenous lookups with std::map (NFC) (llvm#115590)

Heterogenous lookups allow us to call find with StringRef, avoiding a
temporary heap allocation of std::string.

(cherry picked from commit c3c424d)

Author: kazutakahirata

lldb/tools/lldb-dap/DAP.cpp

@@ -694,7 +694,7 @@ bool DAP::HandleObject(const llvm::json::Object &object) {
   const auto packet_type = GetString(object, "type");
   if (packet_type == "request") {
     const auto command = GetString(object, "command");
-    auto handler_pos = request_handlers.find(std::string(command));
+    auto handler_pos = request_handlers.find(command);
     if (handler_pos != request_handlers.end()) {
       handler_pos->second(object);
       return true; // Success

lldb/tools/lldb-dap/DAP.h

@@ -171,7 +171,7 @@ struct DAP {
   // the old process here so we can detect this case and keep running.
   lldb::pid_t restarting_process_id;
   bool configuration_done_sent;
-  std::map<std::string, RequestCallback> request_handlers;
+  std::map<std::string, RequestCallback, std::less<>> request_handlers;
   bool waiting_for_run_in_terminal;
   ProgressEventReporter progress_event_reporter;
   // Keep track of the last stop thread index IDs as threads won't go away