[Alias] Add 're' alias for register

[JDevlieghere]

Summary

This patch makes re an alias for register. Currently re<TAB> gives you the choice between register and reproducer. Given that you use register a lot more often, register should win for the common substring.

[jingham]

LGTM

packages/Python/lldbsuite/test/functionalities/register/register_command/TestRegisters.py

def write_and_read(self, frame, register, new_value, must_exist=True):
         if must_exist:
             self.assertTrue(
                 value.IsValid(),
                 "finding a value for register " +
                 register)
         elif not value.IsValid():
             return  # If register doesn't exist, skip this test
 
-        self.runCmd("register write " + register + " \'" + new_value + "\'")
+        # Also test the 're' alias.
+        self.runCmd("re write " + register + " \'" + new_value + "\'")
         self.expect(
             "register read " +
             register,
             substrs=[
                 register +
                 ' = ',
                 new_value])
 

source/Interpreter/CommandInterpreter.cpp

#endif
   }
 
   cmd_obj_sp = GetCommandSPExact("frame variable", false);
   if (cmd_obj_sp) {
     AddAlias("v", cmd_obj_sp);
     AddAlias("var", cmd_obj_sp);
     AddAlias("vo", cmd_obj_sp, "--object-description");
   }
+
+  cmd_obj_sp = GetCommandSPExact("register", false);
+  if (cmd_obj_sp) {
+    AddAlias("re", cmd_obj_sp);
+  }
 }
 
 void CommandInterpreter::Clear() {
   m_command_io_handler_sp.reset();
 }
 
 const char *CommandInterpreter::ProcessEmbeddedScriptCommands(const char *arg) {
   // This function has not yet been implemented.