[BUG] Field of Alias type in PPL does not work as expected

[qianheng-aws]

What is the bug?
For field of alias type maps to a nested field, it cannot work as expected.

How can one reproduce the bug?

1. Create index with mapping:

PUT /test
{
  "mappings": {
      "properties": {
        "log": {
          "properties": {
            "url": {
              "properties": {
                "message": {
                  "type": "text",
                  "fields": {
                    "keyword": {
                      "type": "keyword",
                      "ignore_above": 256
                    }
                  }
                },
                "time": {
                  "type": "long"
                }
              }
            }
          }
        },
        "message_alias": {
            "type": "alias",
            "path": "log.url.message"
          
        },
        "time_alias": {
           "type": "alias",
            "path": "log.url.time"
        }
      }
    }
}

2. Add doc:

POST /test/_doc
{"log": {"url": {"message": "/e2e/h/zap", "time": 1} } }

3. query source=test | where message_alias = "/e2e/h/zap" failed with exception:

Caused by: java.lang.IllegalStateException: Cannot find the path [log.url.message] for alias type field [message_alias]
        at org.opensearch.sql.opensearch.data.type.OpenSearchDataType.lambda$parseMapping$4(OpenSearchDataType.java:142) ~[?:?]
        at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:986) ~[?:?]
        at org.opensearch.sql.opensearch.data.type.OpenSearchDataType.parseMapping(OpenSearchDataType.java:136) ~[?:?]
        at org.opensearch.sql.opensearch.mapping.IndexMapping.<init>(IndexMapping.java:32) ~[?:?]
        at org.opensearch.sql.opensearch.client.OpenSearchNodeClient.lambda$getIndexMappings$2(OpenSearchNodeClient.java:92) ~[?:?]
        at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180) ~[?:?]
        at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169) ~[?:?]
        at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet.lambda$entryConsumer$0(Collections.java:1778) ~[?:?]
        at java.base/java.util.HashMap$EntrySpliterator.forEachRemaining(HashMap.java:1858) ~[?:?]
        at java.base/java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet$UnmodifiableEntrySetSpliterator.forEachRemaining(Collections.java:1803) ~[?:?]
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509) ~[?:?]
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) ~[?:?]
        at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921) ~[?:?]
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:?]
        at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682) ~[?:?]