Function names are case-sensitive

[jordanw-bq]

Using Docker image amazon/opendistro-for-elasticsearch:1.1.0
Dataset: Flights sample data (loaded through Kibana)
SQL Plugin version: 1.1.0.1

Example Query:
SELECT SUBSTRING(OriginWeather, 1, 2) FROM kibana_sample_data_flights

Result:

Internal Server Error. Reason: There was internal problem at backend. Type: UnsupportedOperationException. Details: The following method is not supported in Schema: SUBSTRING
	at com.amazon.opendistroforelasticsearch.jdbc.StatementImpl.executeQueryRequest(StatementImpl.java:78)
	at com.amazon.opendistroforelasticsearch.jdbc.StatementImpl.executeQueryX(StatementImpl.java:61)
	at com.amazon.opendistroforelasticsearch.jdbc.StatementImpl.execute(StatementImpl.java:170)

Note:
SELECT substring(OriginWeather, 1, 2)... returns results as intended.

Expectation:
Tableau will use UPPERCASE function names in almost all cases. Casing should not matter for function names in a query.

[dai-chen]

Actually both our old and new parser are case-insensitive to function name. This issue is similar as #224 and thrown from our JDBC formatter.

[dai-chen]

Just checked our formatter seems match function name in case sensitive way (simply look it up in hash set).

[galkk]

related to #176