[SPARK-20145] Fix range case insensitive bug in SQL

## What changes were proposed in this pull request?
Range in SQL should be case insensitive

## How was this patch tested?
unit test

Author: samelamin <hussam.elamin@gmail.com>
Author: samelamin <sam_elamin@discovery.com>

Closes #17487 from samelamin/SPARK-20145.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveTableValuedFunctions.scala

@@ -17,9 +17,7 @@
 
 package org.apache.spark.sql.catalyst.analysis
 
-import org.apache.spark.{SparkConf, SparkContext}
 import org.apache.spark.sql.catalyst.expressions.Expression
-import org.apache.spark.sql.catalyst.plans._
 import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, Range}
 import org.apache.spark.sql.catalyst.rules._
 import org.apache.spark.sql.types.{DataType, IntegerType, LongType}
@@ -105,7 +103,7 @@ object ResolveTableValuedFunctions extends Rule[LogicalPlan] {
 
   override def apply(plan: LogicalPlan): LogicalPlan = plan resolveOperators {
     case u: UnresolvedTableValuedFunction if u.functionArgs.forall(_.resolved) =>
-      builtinFunctions.get(u.functionName) match {
+      builtinFunctions.get(u.functionName.toLowerCase()) match {
         case Some(tvf) =>
           val resolved = tvf.flatMap { case (argList, resolver) =>
             argList.implicitCast(u.functionArgs) match {

sql/core/src/test/resources/sql-tests/inputs/table-valued-functions.sql

@@ -18,3 +18,9 @@ select * from range(1, 1, 1, 1, 1);
 
 -- range call with null
 select * from range(1, null);
+
+-- range call with a mixed-case function name
+select * from RaNgE(2);
+
+-- Explain
+EXPLAIN select * from RaNgE(2);

sql/core/src/test/resources/sql-tests/results/table-valued-functions.sql.out

 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 7
+-- Number of queries: 9
 
 
 -- !query 0
@@ -85,3 +85,21 @@ struct<>
 -- !query 6 output
 java.lang.IllegalArgumentException
 Invalid arguments for resolved function: 1, null
+
+
+-- !query 7
+select * from RaNgE(2)
+-- !query 7 schema
+struct<id:bigint>
+-- !query 7 output
+0
+1
+
+
+-- !query 8
+EXPLAIN select * from RaNgE(2)
+-- !query 8 schema
+struct<plan:string>
+-- !query 8 output
+== Physical Plan ==
+*Range (0, 2, step=1, splits=None)