[lldb-vscode] Use a switch to avoid else-after-return (NFC)

[JDevlieghere]

Summary

Use a switch to avoid else-after-return.

[wallace]

Thanks!

lldb/tools/lldb-vscode/ProgressEvent.cpp

 //===-- ProgressEvent.cpp ---------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "ProgressEvent.h"
 
 #include "JSONUtils.h"
+#include "llvm/Support/ErrorHandling.h"
 #include <optional>
 
 using namespace lldb_vscode;
 using namespace llvm;
 
 // The minimum duration of an event for it to be reported
 const std::chrono::duration<double> kStartProgressEventReportDelay =
     std::chrono::seconds(1);
bool ProgressEvent::EqualsForIDE(const ProgressEvent &other) const {
   return m_progress_id == other.m_progress_id &&
          m_event_type == other.m_event_type &&
          m_percentage == other.m_percentage;
 }
 
 ProgressEventType ProgressEvent::GetEventType() const { return m_event_type; }
 
 StringRef ProgressEvent::GetEventName() const {
-  if (m_event_type == progressStart)
+  switch (m_event_type) {
+  case progressStart:
     return "progressStart";
-  else if (m_event_type == progressEnd)
-    return "progressEnd";
-  else
+  case progressUpdate:
     return "progressUpdate";
+  case progressEnd:
+    return "progressEnd";
+  }
+  llvm_unreachable("All cases handled above!");
 }
 
 json::Value ProgressEvent::ToJSON() const {
   llvm::json::Object event(CreateEventObject(GetEventName()));
   llvm::json::Object body;
 
   std::string progress_id_str;
   llvm::raw_string_ostream progress_id_strm(progress_id_str);