Make RangeTblEntry dump order consistent

Make RangeTblEntry dump order consistent

Put the fields alias and eref earlier in the struct, so that it
matches the order in _outRangeTblEntry()/_readRangeTblEntry().  This
helps if we ever want to fully automate out/read of RangeTblEntry.
Also, it makes dumps in the debugger easier to read in the same way.
Internally, this makes no difference.

Reviewed-by: Andrew Dunstan 
Discussion: https://www.postgresql.org/message-id/flat/4b27fc50-8cd6-46f5-ab20-88dbaadca645@eisentraut.org