Introduction

This PR extends support for @JS protocol by adding support for protocol properties, Optional and additional support on types not previously supported, because of lack of the ImportTS side.

Overview

• Added support for get/set properties in @JS protocol declarations
• Properties can now be accessed and modified on protocol implementations from JavaScript
• Supports all exportable types including primitives, strings, enums (case/raw value/associated value), Optionals and Swift heap objects

Testing

Added comprehensive tests in Tests/BridgeJSRuntimeTests/ExportAPITests.swift:

• Protocol with various optional property types
• Direct property access from Swift side
• Protocol implementation testing
• All optional type combinations
  As I run into quite few issues along the way, I wanted to keep large test set, especially due to amount of new lifting / lowering methods added and use cases to test.

Documentation

Updated Sources/JavaScriptKit/Documentation.docc/Articles/BridgeJS/Exporting-Swift/Exporting-Swift-Protocols.md

Technical Details

I had few attempts at proper support for optionals and properties, but this is what I ended up with, was not able to simplify approach further while keeping it sensible, but any suggestions on improvements here are welcomed 🙏🏻

The implementation uses two different strategies for handling optional types in protocol properties, determined by WebAssembly ABI constraints:

1. Sentinel Values (Single Return Value)
   Used when the WASM ABI can distinguish null from valid values using a sentinel:

• Optional<Bool>: Uses -1 for nil, 0 for false, 1 for true
• Optional<CaseEnum>: Uses -1 for nil, 0+ for enum cases
• Optional<AssociatedValueEnum>: Uses -1 for nil, 0+ for case IDs
• Optional<SwiftHeapObject>: Uses 0 (null pointer) for nil

2. Side-Channel
   Used when WASM ABI cannot distinguish null from valid values (e.g., any valid value is possible):

• Optional<Int>
• Optional<Float>
• Optional<Double>
• Optional<String>
• Optional<RawValueEnum>

Side-channel uses global storage variables (tmpRetOptionalInt, tmpRetString, etc.) that are set by the getter and read by the lifting code.

Some new methods were required in BridgeJSIntrinsic, besides the one we used for most of the lifting / lowering:

1. bridgeJSLowerParameterWithPresence(): Converts optional to (isSome, value) tuple for protocol setters/parameters
2. bridgeJSLiftReturnFromSideChannel(): Lifts optionals from side-channel storage for protocol property getters
   For sentinel-based lifting for types that support it, I added implementation for bridgeJSLiftReturn(_ value: T):