[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/ScriptedProcessPythonInterface.cpp

@@ -76,10 +76,10 @@ Status ScriptedProcessPythonInterface::Stop() {
   return GetStatusFromMethod("stop");
 }
 
-llvm::Optional<MemoryRegionInfo>
+std::optional<MemoryRegionInfo>
 ScriptedProcessPythonInterface::GetMemoryRegionContainingAddress(
     lldb::addr_t address, Status &error) {
-  auto mem_region = Dispatch<llvm::Optional<MemoryRegionInfo>>(
+  auto mem_region = Dispatch<std::optional<MemoryRegionInfo>>(
       "get_memory_region_containing_address", error, address);
 
   if (error.Fail()) {
@@ -170,7 +170,7 @@ bool ScriptedProcessPythonInterface::IsAlive() {
   return obj->GetBooleanValue();
 }
 
-llvm::Optional<std::string>
+std::optional<std::string>
 ScriptedProcessPythonInterface::GetScriptedThreadPluginName() {
   Status error;
   StructuredData::ObjectSP obj = Dispatch("get_scripted_thread_plugin", error);