Support accepting the interval keyword in the schema string

import org.apache.spark.sql.types._
import org.apache.spark.sql.catalyst.expressions._

Cast(Literal("interval 3 month 1 hours"), CalendarIntervalType).eval()
res0: Any = interval 3 months 1 hours

scala> spark.sql("SELECT CAST('interval 3 month 1 hour' AS interval)").show
org.apache.spark.sql.catalyst.parser.ParseException:
DataType interval is not supported.(line 1, pos 41)

== SQL ==
SELECT CAST('interval 3 month 1 hour' AS interval)
-----------------------------------------^^^

  at org.apache.spark.sql.catalyst.parser.AstBuilder.$anonfun$visitPrimitiveDataType$1(AstBuilder.scala:1931)
  at org.apache.spark.sql.catalyst.parser.ParserUtils$.withOrigin(ParserUtils.scala:108)
  at org.apache.spark.sql.catalyst.parser.AstBuilder.visitPrimitiveDataType(AstBuilder.scala:1909)
  at org.apache.spark.sql.catalyst.parser.AstBuilder.visitPrimitiveDataType(AstBuilder.scala:52)
  at org.apache.spark.sql.catalyst.parser.SqlBaseParser$PrimitiveDataTypeContext.accept(SqlBaseParser.java:15397)
  at org.apache.spark.sql.catalyst.parser.AstBuilder.typedVisit(AstBuilder.scala:58)
  at org.apache.spark.sql.catalyst.parser.AstBuilder.visitSparkDataType(AstBuilder.scala:1903)
  at org.apache.spark.sql.catalyst.parser.AstBuilder.$anonfun$visitCast$1(AstBuilder.scala:1334)