[Bug] Support Multi-fields in WHERE Conditions

What is the bug?
There is limitation on Multi-fields in WHERE Conditions

If a field is defined with multiple types, then SQL engine treat it as text_keyword.

How can one reproduce the bug?
For example if the field defined as

"id1" : {
          "type" : "keyword",
          "fields" : {
            "id2" : {
              "type" : "integer"
            }
          }
        },

then following query

SELECT id1 
FROM sample_data 
WHERE n1 IN ('19') AND n2 IN ('299')
ORDER BY id1.id2 ASC LIMIT 10 OFFSET 0

will result in error

{
  "error": {
    "reason": "Invalid SQL query",
    "details": "can't resolve Symbol(namespace=FIELD_NAME, name=id1.id2) in type env",
    "type": "SemanticCheckException"
  },
  "status": 400
}

What is the expected behavior?
For multi-field (a text field with another keyword field inside), there should be no assumption that the keyword field name is always "keyword".

Query with above format should return expected result.

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22]
• Plugins

Do you have any screenshots?
If applicable, add screenshots to help explain your problem.

Do you have any additional context?
Add any other context about the problem.

Start with opensearch/src/main/java/org/opensearch/sql/opensearch/mapping/IndexMapping.java around the linked line, then review the multi-fields documentation and reproduce the query against the example mapping. Trace how the nested id1.id2 field is resolved and add coverage for a non-keyword multi-field. Done means the query returns the expected result without assuming the child field is named keyword.