[lldb] Fix deadlock between statusline and output mutex

Fix a deadlock between the statusline mutex (in Debugger) and the output
file mutex (in LockedStreamFile). The deadlock occurs when the main
thread is calling the statusline callback while holding the output mutex
in Editline, while the default event thread is trying to update the
stausline.

rdar://149251156

Author: JDevlieghere

lldb/source/Host/common/Editline.cpp

@@ -567,8 +567,11 @@ int Editline::GetCharacter(EditLineGetCharType *c) {
     m_needs_prompt_repaint = false;
   }
 
-  if (m_redraw_callback)
+  if (m_redraw_callback) {
+    m_locked_output.reset();
     m_redraw_callback();
+    m_locked_output.emplace(m_output_stream_sp->Lock());
+  }
 
   if (m_multiline_enabled) {
     // Detect when the number of rows used for this input line changes due to