Re-engineer the code for post-join operations

<SanjaByelkin> instead of creating new JOIN_TABs array (i.e. new plan) to process results in temporary table (GROUPING ORDERING)
<SanjaByelkin> just additional JOIN_TABs added at the end which represent such operation
<SanjaByelkin> so you never rewrite it
<SanjaByelkin> it is backport from MySQL
<SanjaByelkin> so you can add any number of postprocessing operations
<SanjaByelkin> and he need it for window functions