[lldb] Use std::optional instead of llvm::Optional (NFC)

This patch replaces (llvm::|)Optional< with std::optional<.  I'll post
a separate patch to clean up the "using" declarations, #include
"llvm/ADT/Optional.h", etc.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

lldb/source/Plugins/ScriptInterpreter/Python/ScriptedThreadPythonInterface.cpp

@@ -71,7 +71,7 @@ lldb::tid_t ScriptedThreadPythonInterface::GetThreadID() {
   return obj->GetIntegerValue(LLDB_INVALID_THREAD_ID);
 }
 
-llvm::Optional<std::string> ScriptedThreadPythonInterface::GetName() {
+std::optional<std::string> ScriptedThreadPythonInterface::GetName() {
   Status error;
   StructuredData::ObjectSP obj = Dispatch("get_name", error);
 
@@ -91,7 +91,7 @@ lldb::StateType ScriptedThreadPythonInterface::GetState() {
   return static_cast<StateType>(obj->GetIntegerValue(eStateInvalid));
 }
 
-llvm::Optional<std::string> ScriptedThreadPythonInterface::GetQueue() {
+std::optional<std::string> ScriptedThreadPythonInterface::GetQueue() {
   Status error;
   StructuredData::ObjectSP obj = Dispatch("get_queue", error);
 
@@ -134,8 +134,7 @@ StructuredData::DictionarySP ScriptedThreadPythonInterface::GetRegisterInfo() {
   return dict;
 }
 
-llvm::Optional<std::string>
-ScriptedThreadPythonInterface::GetRegisterContext() {
+std::optional<std::string> ScriptedThreadPythonInterface::GetRegisterContext() {
   Status error;
   StructuredData::ObjectSP obj = Dispatch("get_register_context", error);