[lldb] Remove Debugger::Get{Output,Error}Stream (NFC) (#126821)

Remove Debugger::GetOutputStream and Debugger::GetErrorStream in
preparation for replacing both with a new variant that needs to be
locked and hence can't be handed out like we do right now.

The patch replaces most uses with GetAsyncOutputStream and
GetAsyncErrorStream respectively. There methods return new StreamSP
objects that automatically get flushed on destruction.

See #126630 for more details.

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

@@ -1910,10 +1910,10 @@ bool ScriptInterpreterPythonImpl::BreakpointCallbackFunction(
             llvm::handleAllErrors(
                 maybe_ret_val.takeError(),
                 [&](PythonException &E) {
-                  debugger.GetErrorStream() << E.ReadBacktrace();
+                  *debugger.GetAsyncErrorStream() << E.ReadBacktrace();
                 },
                 [&](const llvm::ErrorInfoBase &E) {
-                  debugger.GetErrorStream() << E.message();
+                  *debugger.GetAsyncErrorStream() << E.message();
                 });
 
           } else {