IMPALA-14405: Labels for Calcite expressions not matching original planner

Calcite sets literal expressions to EXPR$<x> which did not match
expressions given by the Impala planner. For literal expressions
such as "select 1 + 1", Impala creates the column name as "1 + 1".

The field names can be found in the abstract syntax tree, so
they are not set within the CalciteRelNodeConverter before the
logical tree is created.

A small test was added to calcite.test for a basic sanity check,
but more comprehensive tests will be run in the tests/shell module
(e.g. in test_shell_commandline.py and test_shell_interactive) which
contain tests for labels.

Change-Id: Ibd3e6366a284f53807b4b2c42efafa279249c1ea
Reviewed-on: http://gerrit.cloudera.org:8080/23516
Reviewed-by: Steve Carlin <scarlin@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>

testdata/workloads/functional-query/queries/QueryTest/calcite.test

@@ -1097,3 +1097,27 @@ select ndv(varchar_col, 0) from functional.chars_medium;
 ---- CATCH
 Error in NDV function, second parameter needs to be between 1 and 10.
 ====
+---- QUERY
+# Labels test
+select 2, 1 + 1;
+---- LABELS
+2,1 + 1
+---- RESULTS
+2,2
+---- TYPES
+tinyint,smallint
+---- RUNTIME_PROFILE
+row_regex: .*PlannerType: CalcitePlanner.*
+====
+---- QUERY
+# Labels test
+select length('hello')
+---- LABELS
+length('hello')
+---- RESULTS
+5
+---- TYPES
+int
+---- RUNTIME_PROFILE
+row_regex: .*PlannerType: CalcitePlanner.*
+====