Unified: Drop the separate swift-syntax binary and make tests runnable both with Bazel and cargo

[jketema]

Partially based on: #22248

Note that this doesn't yet update the .md files. I'll deal with those in a separate PR. Also building on macOS from the internal repo is still broken (will deal with that after this has been merged). I also have not looked at create-extractor-pack.sh yet.

Commit-by-commit review recommended.

[Copilot]

Pull request overview

Integrates Swift parsing directly into the unified extractor and enables its tests under both Bazel and Cargo.

Changes:

• Replaces the external parser process with direct swift-syntax-rs calls.
• Adds Swift linking, runtime packaging, and platform constraints.
• Adds Bazel targets for corpus and pipeline tests.

Show a summary per file

File	Description
Cargo.lock	Records the new extractor dependency.
unified/BUILD.bazel	Packages the extractor with Swift runtime libraries.
unified/platforms.bzl	Defines supported unified-extractor platforms.
unified/extractor/BUILD.bazel	Links Swift and adds Bazel tests.
unified/extractor/Cargo.toml	Adds swift-syntax-rs.
unified/extractor/build.rs	Propagates Cargo linker metadata.
unified/extractor/src/languages/swift/parse.rs	Calls Swift parsing in-process.
unified/extractor/tests/corpus_tests.rs	Supports Bazel and Cargo corpus paths.
unified/swift-syntax-rs/BUILD.bazel	Simplifies binary and runtime linking targets.
unified/swift-syntax-rs/Cargo.toml	Declares the native library link name.
unified/swift-syntax-rs/build.rs	Exposes native library/runtime directories.
unified/swift-syntax-rs/swift-syntax-parse.sh	Removes the obsolete parser wrapper.

Review details

• Files reviewed: 11/12 changed files
• Comments generated: 2
• Review effort level: Balanced

[redsun82]

I like the approach! I even wonder whether we could generalize with unconditionally passing --cfg=bazel to all bazel rust invocations (via a .bazelrc/.internal.bazelrc setting maybe?).

[jketema]

I like the approach! I even wonder whether we could generalize with unconditionally passing --cfg=bazel to all bazel rust invocations (via a .bazelrc/.internal.bazelrc setting maybe?).

Are there other places where that would be immediately useful?