[BUG] PPL does not support querying Alias fields

[ashwin-pc]

What is the bug?
When querying using PPL but there is an alias field in the filter clause. The query fails.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

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

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

[penghuo]

could u add more context? sample query and sample data to reporduce the issue.

[xinyual]

I can provide a sample

PUT /try
{
    "mappings":{
        "properties": {
            "time1": {
                "type": "date"
            },
            "time2": {
                "type": "alias",
                "path": "time1"
            }
        }
    }
}

POST /_plugins/_ppl/
{
    "query": "source=try | fields `time2`"
}

It shows

{
  "error": {
    "reason": "Invalid Query",
    "details": "can't resolve Symbol(namespace=FIELD_NAME, name=time2) in type env",
    "type": "SemanticCheckException"
  },
  "status": 400
}