Support ordinal aliases in GROUP and ORDER BY clauses

[abbashus]

Issue #215

Description of changes:

• Added a new Rewriter to map GROUP BY and ORDER By aliases to SELECT column fields

Testing

• Passing Gradle build with existing unit and integration tests
• Added new unit tests and integration tests

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[galkk]

I like this approach. In theory, it could be used to inline/fix aliases as well, in order by/group by expressions, instead of hackier approach that we have now (something that I've tried to do in https://github.com/opendistro-for-elasticsearch/sql/pull/168/files, that I needed to revert later)

[galkk]

I don't understand why we've supposedly have the same check twice, could you add more comments explaining what's going on? From the code it looks like this checks if we have ordinals, and the code below does the same, but in different way, on parsed raw sql query. Could only one check work? Why we need to parse sql again?

In general, could you add better description of algorithm into the PR or into javadoc, with examples. I find the intention of the code a bit hard to follow

[abbashus]

Added some comments to help understand the code better. Removed the redundant check.

[galkk]

this is a bit repetitive, you can extract this to method like

getExpressionByOrdinal

and throw an exception inside (will simplify code a bt). Same for visiting group by expressions

[abbashus]

Refactored it into checkAndGet method.

[davidcui1225]

LGTM