Add tree-sitter-swift extractor scaffolding and YEAST desugaring

[asgerf]

• Adds boilerplate for a tree-sitter based extractor using tree-sitter-swift.
• Uses YEAST to perform a dummy desugaring.
• A CodeQL test verifies that the desugaring is happening.
• Adds AGENTS.md to help with worktrees

The extractor is placed in a folder called unified because the intent is to have more languages in there eventually.

Some follow-up work I have not included in the PR but working on:

• Corpus-style extractor tests with schema validation
• Changing the output schema

[asgerf]

Rerun has been triggered: 1 restarted 🚀

• CPP Integration tests Linux

[asgerf]

Rerun has been triggered, but no failed runs found ⚠️

[Copilot]

Pull request overview

This PR introduces an initial “unified” tree-sitter-based extractor scaffold (currently targeting Swift via tree-sitter-swift), wires in a simple YEAST desugaring pass, and adds a small CodeQL library-test to confirm the desugaring is applied during extraction.

Changes:

• Add a new Rust-based unified extractor binary with extract, generate, and autobuild subcommands.
• Add packaging/build integration (Bazel + Cargo workspace) and helper scripts for local pack generation and qltest indexing.
• Add a basic unified QL pack/test pack and a Swift library-test verifying the desugaring effect.

Show a summary per file

File	Description
unified/tools/qltest.sh	Adds qltest indexing for Swift-related extensions in unified tests.
unified/tools/qltest.cmd	Windows equivalent qltest indexing script for unified.
unified/tools/index-files.sh	Hooks CodeQL “index-files” into the unified extractor’s extract subcommand.
unified/tools/index-files.cmd	Windows equivalent for unified index-files.
unified/tools/BUILD.bazel	Packages unified tool scripts into the extractor pack.
unified/tools/autobuild.sh	Runs unified extractor autobuild.
unified/tools/autobuild.cmd	Windows equivalent for unified autobuild.
unified/scripts/create-extractor-pack.sh	Local script to build and assemble an extractor pack for testing.
unified/ql/test/qlpack.yml	Defines the unified test pack and its workspace dependencies.
unified/ql/test/qlpack.lock.yml	Lockfile for unified test pack.
unified/ql/test/library-tests/BasicTest/test.swift	Swift input used by the library-test.
unified/ql/test/library-tests/BasicTest/test.ql	Library-test query predicates validating AST/desugaring behavior.
unified/ql/test/library-tests/BasicTest/test.expected	Expected results validating the desugaring effect.
unified/ql/src/qlpack.yml	Defines the unified queries pack.
unified/ql/src/qlpack.lock.yml	Lockfile for unified queries pack.
unified/ql/lib/unified.dbscheme.stats	Initial dbscheme stats file for unified.
unified/ql/lib/qlpack.yml	Defines the unified library pack and dbscheme wiring.
unified/ql/lib/qlpack.lock.yml	Lockfile for unified library pack.
unified/ql/lib/codeql/unified/Ast.qll	Generated Swift AST library produced from tree-sitter node types.
unified/ql/lib/codeql/Locations.qll	Adds a minimal locations helper library for unified QL.
unified/ql/lib/codeql/files/FileSystem.qll	Adds minimal file system abstractions for unified QL.
unified/ql/lib/BUILD.bazel	Bazel packaging targets for unified dbscheme artifacts.
unified/extractor/src/main.rs	CLI entrypoint wiring extract/generate/autobuild.
unified/extractor/src/languages/swift/swift.rs	Swift language spec, including a YEAST desugaring phase.
unified/extractor/src/generator.rs	Generates dbscheme/QL library for the Swift grammar.
unified/extractor/src/extractor.rs	Unified extractor implementation using the shared tree-sitter extractor framework.
unified/extractor/src/autobuilder.rs	Unified autobuilder wrapper around shared autobuilder support.
unified/extractor/Cargo.toml	New crate definition and dependencies for unified extractor.
unified/extractor/BUILD.bazel	Bazel build rule for the unified Rust extractor binary.
unified/codeql-extractor.yml	Declares the new unified extractor metadata and file types.
unified/BUILD.bazel	Bazel packaging rule to assemble the unified extractor pack.
unified/AGENTS.md	Contributor instructions for building/testing the unified extractor.
unified/.gitignore	Ignores local build/test outputs for unified.
MODULE.bazel	Adds tree-sitter-swift vendored repo to Bazel module deps.
misc/bazel/3rdparty/tree_sitter_extractors_deps/defs.bzl	Adds unified extractor crate dependency mapping and swift crate repo.
misc/bazel/3rdparty/tree_sitter_extractors_deps/BUILD.tree-sitter-swift-0.7.2.bazel	Generated Bazel BUILD for tree-sitter-swift crate.
misc/bazel/3rdparty/tree_sitter_extractors_deps/BUILD.bazel	Adds aliases for the tree-sitter-swift crate.
Cargo.toml	Adds unified/extractor to the workspace members.
Cargo.lock	Adds lock entries for codeql-extractor-unified and tree-sitter-swift.

Copilot's findings

• Files reviewed: 37/40 changed files
• Comments generated: 6