[gn build] Port 82264d2

Author: llvmgnsyncbot

llvm/utils/gn/secondary/lldb/tools/lldb-dap/BUILD.gn

@@ -57,8 +57,12 @@ executable("lldb-dap") {
     "Handler/ExceptionInfoRequestHandler.cpp",
     "Handler/InitializeRequestHandler.cpp",
     "Handler/LaunchRequestHandler.cpp",
+    "Handler/NextRequestHandler.cpp",
     "Handler/RequestHandler.cpp",
     "Handler/RestartRequestHandler.cpp",
+    "Handler/StepInRequestHandler.cpp",
+    "Handler/StepInTargetsRequestHandler.cpp",
+    "Handler/StepOutRequestHandler.cpp",
     "IOStream.cpp",
     "InstructionBreakpoint.cpp",
     "JSONUtils.cpp",