feat(cosmosdb): improve grammar compatibility

[h3n4l]

Summary

• Add missing CosmosDB SQL syntax: ?? coalesce, <> inequality, LIKE ESCAPE, ARRAY(subquery), -- line comments, Infinity/NaN constants, c[@param] bracket parameter access
• Rework FROM clause to support ROOT, subroot paths (container.property), IN iteration, subqueries, and flexible JOINs
• Expand keyword-as-identifier support: 17 keywords usable as property names after dot (e.g., c.select, c.from, c.where)
• Add ORDER BY RANK for full-text search syntax

References

• Official docs: https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/query/
• Azure ANTLR grammar: https://github.com/Azure/cosmos-sql-language-service (archived)
• Vercel PEG parser: https://github.com/vercel/cosmosdb-query

Validation

All new syntax features validated against the CosmosDB emulator (Docker mcr.microsoft.com/cosmosdb/linux/azure-cosmos-emulator:vnext-preview). Full-text search functions are grammar-only (emulator doesn't support them yet).

Test plan

• All 37 parser tests pass (23 existing + 14 new example SQL files)
• Emulator validation for: ??, <>, LIKE ESCAPE, ARRAY(subquery), FROM ROOT, FROM (subquery), -- comments, JOIN IN

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR updates the CosmosDB ANTLR grammar (lexer + parser) to accept additional Cosmos DB NoSQL SQL syntax variants and adds new example SQL files to exercise those grammar paths via the existing parser test harness.

Changes:

• Extend lexer/parser grammar to support additional operators/constructs (e.g., ??, <>, LIKE ... ESCAPE, ARRAY(subquery), ROOT, RANK, -- comments, Infinity/NaN, bracket parameter indexing).
• Rework FROM/JOIN grammar to support additional FROM sources (e.g., ROOT, subroot paths, IN iteration, subqueries).
• Add new cosmosdb/examples/*.sql fixtures covering the new syntax.

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
cosmosdb/CosmosDBLexer.g4	Adds new keywords/tokens (ESCAPE, ARRAY, ROOT, RANK, ??, <>, Infinity, NaN, -- line comments).
cosmosdb/CosmosDBParser.g4	Updates grammar rules for ORDER BY RANK, expanded FROM/JOIN forms, LIKE ... ESCAPE, ?? coalesce, bracket-parameter access, ARRAY(subquery), and new constants/operators.
cosmosdb/cosmosdb_lexer.go	Regenerated Go lexer to reflect updated lexer grammar token set.
cosmosdb/examples/array_subquery.sql	Example for ARRAY(subquery) expression.
cosmosdb/examples/bracket_parameter.sql	Example for c[@param] bracket parameter access.
cosmosdb/examples/coalesce_operator.sql	Example for ?? coalesce operator.
cosmosdb/examples/from_in_iteration.sql	Example for FROM <id> IN <path> iteration.
cosmosdb/examples/from_root.sql	Example for FROM ROOT source.
cosmosdb/examples/from_subquery.sql	Example for FROM (subquery) AS alias.
cosmosdb/examples/from_subroot.sql	Example for dotted subroot container path (container.property).
cosmosdb/examples/fulltext_search.sql	Example for ORDER BY RANK ... full-text-search-style ordering.
cosmosdb/examples/infinity_nan.sql	Example for Infinity / NaN constants.
cosmosdb/examples/join_subquery.sql	Example for JOIN <id> IN <expr> join iteration.
cosmosdb/examples/keyword_property_names.sql	Example for keyword-like property access patterns.
cosmosdb/examples/like_escape.sql	Example for LIKE ... ESCAPE ....
cosmosdb/examples/line_comment.sql	Example for -- line comments.
cosmosdb/examples/not_equal_diamond.sql	Example for <> not-equal operator.

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