[lldb-dap] Ensure we acquire the SB API lock while handling requests. (#137026)

Acquiring the lock for the target should help ensure consistency with
other background operations, like the thread monitoring events that can
trigger run commands from a different thread.

Author: ashgti

lldb/tools/lldb-dap/Handler/RequestHandler.cpp

@@ -14,6 +14,7 @@
 #include "Protocol/ProtocolBase.h"
 #include "RunInTerminal.h"
 #include "llvm/Support/Error.h"
+#include <mutex>
 
 #if !defined(_WIN32)
 #include <unistd.h>
@@ -180,6 +181,9 @@ void BaseRequestHandler::Run(const Request &request) {
     return;
   }
 
+  lldb::SBMutex lock = dap.GetAPIMutex();
+  std::lock_guard<lldb::SBMutex> guard(lock);
+
   // FIXME: After all the requests have migrated from LegacyRequestHandler >
   // RequestHandler<> we should be able to move this into
   // RequestHandler<>::operator().