[BUG] Pushdown not work when aggregate on text data type with function `FIRST`/`LAST`/`TAKE`

[LantaoJin]

What is the bug?
Pushdown not work when aggregate on text data type with function FIRST/LAST

How can one reproduce the bug?
Create index

PUT good/
{
  "mappings": {
    "properties": {
      "packets_str": { "type": "keyword" }
    }
  }
}
PUT bad/
{
  "mappings": {
    "properties": {
      "packets_str": { "type": "text" }
    }
  }
}

Ingest data

POST good/_bulk
{"index": {}}
{"packets_str":"10"}
{"index": {}}
{"packets_str":"20"}
{"index": {}}
{"packets_str":"30"}
POST bad/_bulk
{"index": {}}
{"packets_str":"10"}
{"index": {}}
{"packets_str":"20"}
{"index": {}}
{"packets_str":"30"}

Query

POST /_plugins/_ppl/_explain?format=yaml
{
    "query": """
    source=good | stats last(packets_str)
    """
}

returns

calcite:
  logical: |
    LogicalSystemLimit(fetch=[10000], type=[QUERY_SIZE_LIMIT])
      LogicalAggregate(group=[{}], last(packets_str)=[LAST($0)])
        LogicalProject(packets_str=[$0])
          CalciteLogicalIndexScan(table=[[OpenSearch, test]])
  physical: |
    EnumerableLimit(fetch=[10000])
      CalciteEnumerableIndexScan(table=[[OpenSearch, test]], PushDownContext=[[AGGREGATION->rel#301:LogicalAggregate.NONE.[](input=RelSubset#300,group={},last(packets_str)=LAST($0))], OpenSearchRequestBuilder(sourceBuilder={"from":0,"size":0,"timeout":"1m","aggregations":{"last(packets_str)":{"top_hits":{"from":0,"size":1,"version":false,"seq_no_primary_term":false,"explain":false,"fields":[{"field":"packets_str"}],"sort":[{"_doc":{"order":"desc"}}]}}}}, requestedTotalSize=2147483647, pageSize=null, startFrom=0)])

But

POST /_plugins/_ppl/_explain?format=yaml
{
    "query": """
    source=bad | stats last(packets_str)
    """
}

returns

calcite:
  logical: |
    LogicalSystemLimit(fetch=[10000], type=[QUERY_SIZE_LIMIT])
      LogicalAggregate(group=[{}], last(packets_str)=[LAST($0)])
        LogicalProject(packets_str=[$0])
          CalciteLogicalIndexScan(table=[[OpenSearch, test2]])
  physical: |
    EnumerableLimit(fetch=[10000])
      EnumerableAggregate(group=[{}], last(packets_str)=[LAST($0)])
        CalciteEnumerableIndexScan(table=[[OpenSearch, test2]], PushDownContext=[[PROJECT->[packets_str]], OpenSearchRequestBuilder(sourceBuilder={"from":0,"timeout":"1m","_source":{"includes":["packets_str"],"excludes":[]}}, requestedTotalSize=2147483647, pageSize=null, startFrom=0)])

What is the expected behavior?
A clear and concise description of what you expected to happen.

What is your host/environment?

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

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