Support for CAST() function

[rupal-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

Query: SELECT cast(dayOfWeek AS FLOAT) AS calculation FROM kibana_sample_data_flights

Result: No data

{[\n]"
  "error": {[\n]"
    "reason": "Invalid SQL query",[\n]"
    "details": "Failed to parse query due to offending symbol [AS] at: 'SELECT cast(dayOfWeek AS' <--- HERE... More details: Expecting tokens in {'SELECT', '('}",[\n]"
    "type": "SyntaxAnalysisException"[\n]"
  },[\n]"
  "status": 400[\n]"
}

Expected Behaviour: Should return all values from column dayOfWeek as float.

[dai-chen]

We removed CAST syntax in new parser grammar because we thought we don't support it. Actually there are UTs in codebase however UT won't run with new parser. Need to add it back.

[dai-chen]

Apart from the changes in grammar, need to add ITs to cover this case.

[dai-chen]

CAST syntax removed accidentally: https://github.com/antlr/grammars-v4/blob/master/mysql/Positive-Technologies/MySqlParser.g4#L2133