[lldb/Lua] Recognize "quit" as a way to exit the script interpreter.

Add a way to quit the interactive script interpreter from a shell tests.
Currently, the only way (that I know) to exit the interactive Lua
interpreter is to send a EOF with CTRL-D. I noticed that the embedded
Python script interpreter accepts quit (while the regular python
interpreter doesn't). I've added a special case to the Lua interpreter
to do the same.

Differential revision: https://reviews.llvm.org/D82272

lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.cpp

@@ -39,6 +39,11 @@ public:
 
   void IOHandlerInputComplete(IOHandler &io_handler,
                               std::string &data) override {
+    if (llvm::StringRef(data).rtrim() == "quit") {
+      io_handler.SetIsDone(true);
+      return;
+    }
+
     if (llvm::Error error = m_script_interpreter.GetLua().Run(data)) {
       *GetOutputStreamFileSP() << llvm::toString(std::move(error));
     }