[lldb] Improve corefile saving ergonomics

[mib]

Summary

This patch improves the way the user can save the process state into a
corefile by adding completion handler that would provide tab completion
for the corefile path and also resolves the corefile path to expand
relative path.

Signed-off-by: Med Ismail Bennani <[e-mail]>

[bulbazord]

LGTM, what do you think @jasonmolenda ?

lldb/source/API/SBProcess.cpp

std::lock_guard<std::recursive_mutex> guard(
       process_sp->GetTarget().GetAPIMutex());
 
   if (process_sp->GetState() != eStateStopped) {
     error.SetErrorString("the process is not stopped");
     return error;
   }
 
   FileSpec core_file(file_name);
+  FileSystem::Instance().Resolve(core_file);
   error.ref() = PluginManager::SaveCore(process_sp, core_file, core_style,
                                         flavor);
 
   return error;
 }
 
 lldb::SBError
 SBProcess::GetMemoryRegionInfo(lldb::addr_t load_addr,

lldb/source/Commands/CommandObjectProcess.cpp

CommandObjectProcessSaveCore(CommandInterpreter &interpreter)
     CommandArgumentData file_arg{eArgTypePath, eArgRepeatPlain};
     m_arguments.push_back({file_arg});
   }
 
   ~CommandObjectProcessSaveCore() override = default;
 
   Options *GetOptions() override { return &m_options; }
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    CommandCompletions::InvokeCommonCompletionCallbacks(
+        GetCommandInterpreter(), lldb::eDiskFileCompletion, request, nullptr);
+  }
+
   class CommandOptions : public Options {
   public:
     CommandOptions() = default;
 
     ~CommandOptions() override = default;
 
     llvm::ArrayRef<OptionDefinition> GetDefinitions() override {
       return llvm::ArrayRef(g_process_save_core_options);
public:
   };
 
 protected:
   bool DoExecute(Args &command, CommandReturnObject &result) override {
     ProcessSP process_sp = m_exe_ctx.GetProcessSP();
     if (process_sp) {
       if (command.GetArgumentCount() == 1) {
         FileSpec output_file(command.GetArgumentAtIndex(0));
+        FileSystem::Instance().Resolve(output_file);
         SaveCoreStyle corefile_style = m_options.m_requested_save_core_style;
         Status error =
             PluginManager::SaveCore(process_sp, output_file, corefile_style,
                                     m_options.m_requested_plugin_name);
         if (error.Success()) {
           if (corefile_style == SaveCoreStyle::eSaveCoreDirtyOnly ||
               corefile_style == SaveCoreStyle::eSaveCoreStackOnly) {
             result.AppendMessageWithFormat(