Add FROM-first query syntax support

[Abdelrahman-358]

Description

This PR implements support for the feature proposed in #17336 by introducing FROM-first query syntax.

Usage Examples

-- Current syntax
SELECT temperature, humidity FROM sensors WHERE time >= 10;

-- FROM-first syntax
FROM sensors SELECT temperature, humidity WHERE time >= 10;

-- Quick exploration (omitting SELECT implies SELECT *)
FROM sensors LIMIT 10;

Implementation Approach

1. Grammar Update
   Add fromFirstQuerySpecification rule to RelationalSql.g4.

2. AST Builder
   Add visitFromFirstQuerySpecification() in AstBuilder.java, reusing the existing visitQuerySpecification() logic, with handling for the omitted SELECT clause (interpreted as SELECT *).

3. Testing
   Add unit and integration tests to cover the new syntax scenarios.

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This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods.
• added or updated version, license, or notice information
• added comments explaining the "why" and the intent of the code wherever would not be obvious
  for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold
  for code coverage.
• added integration tests.
• been tested in a test IoTDB cluster.

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Key changed/added classes (or packages if there are too many classes) in this PR

[Abdelrahman-358]

Hi @JackieTien97 , could you please review this PR when you have time?

I’ve also sent a request to the dev mailing list, but it may have been filtered into the Promotions tab.

[Copilot]

Pull request overview

Adds an additional, DuckDB-style FROM-first query form to IoTDB’s relational SQL dialect, enabling FROM <table> [SELECT ...] ... (with omitted SELECT implying SELECT *) while preserving existing SELECT-first syntax.

Changes:

• Extend the ANTLR grammar to parse FROM-first query specifications as a queryPrimary.
• Add AST builder support to translate FROM-first parse trees into the existing QuerySpecification AST (including implicit SELECT *).
• Add analyzer-level unit tests and a new integration test suite covering basic queries, implicit select, joins, and aggregation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
iotdb-core/relational-grammar/src/main/antlr4/org/apache/iotdb/db/relational/grammar/sql/RelationalSql.g4	Adds fromFirstQuerySpecification and wires it into queryPrimary so queries can start with FROM.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/parser/AstBuilder.java	Builds a QuerySpecification from the new grammar rule, including implicit SELECT * behavior.
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/AnalyzerTest.java	Adds unit tests to ensure FROM-first queries analyze/plan equivalently to SELECT-first equivalents.
integration-test/src/test/java/org/apache/iotdb/relational/it/query/recent/IoTDBFromFirstQueryIT.java	Adds integration coverage for end-to-end execution of FROM-first queries across common patterns.

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