ASTERIXDB-1226: implement SQL++ core group-by semantics and syntatic sugars. -Implmented SQL++ core group-by semantics; -Implemented SQL++ group-by syntatic sugars for standard SQL; -Added test cases; -Fixed column alias rewriter; -Fixed the variable scoping for joins.
SQL++ parser: 1. refactored asterix-aql to become asterix-lang-common and asterix-lang-aql, where the former is the common part for different languages; 2. added asterix-lang-sqlpp on top of asterix-lang-common; 3. ported parser tests, optimizer tests and runtime tests in asterix-app to their sql++ version, and added parser tests for all the queries. Change-Id: Ie5af4e3b692ca017ec047a1ba3b404a51beb3a2e Reviewed-on: https://asterix-gerrit.ics.uci.edu/466 Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu> Reviewed-by: Till Westmann <tillw@apache.org>