Split arguments ignoring extra whitespace in lldb dump (#7149)

The `split(" ")` function will split two consecutive spaces apart,
giving an empty string in its output. So `dump context inst5` was
mis-parsed to have arguments `["context", "", "inst5"]`. If `split()` is
called with no arguments, it splits on whitespace but ignores
consecutive whitespace, so we correctly parse the args to be
`["context", "inst5"]`.

scripts/lldbinit.py

@@ -67,7 +67,7 @@ Example usage:
   dump context() inst42
 """)
 
-    args = command.split(" ")
+    args = command.split()
     if len(args) < 2:
         print_usage()
         return