Consider not performing alias rewrite to the rest of the query when alias is a column name

E.g. `SELECT SUM(a) AS a WHERE a > 10` will throw exception because it will be rewritten to `SELECT SUM(a) AS a WHERE SUM(A) > 10`

Also, seems alias is not allowed in `WHERE` clause in standard SQL: https://docs.oracle.com/cd/E17952_01/mysql-5.7-en/problems-with-alias.html.
Not sure if we should block alias rewrite in `WHERE` clause because it can cause backward incompatible.

Start by reproducing the `SELECT SUM(a) AS a WHERE a > 10` query and tracing Pinot's alias-rewrite entry point. Investigate how alias references in `WHERE` are distinguished from column references, then clarify the compatibility decision and add regression coverage for the chosen behavior.

Written by the indexing model from the issue text.