BridgeJS: Enforce throws(JSException) for @JS protocol properties

[krodak]

Overview

• Require throws(JSException) on @JS protocol property getters, matching the import side (@JSGetter) behavior
• { get set } properties no longer supported - use readonly getter + setter method pattern
• Fix generated protocol wrapper code to include exception checking for property access
• Updated tests and documentation

Test updates

• Protocol.swift test input: Updated properties to { get throws(JSException) } pattern with setter methods
• ExportAPITests.swift: Updated DataProcessor protocol with new property pattern

Documentation

• Updated Exporting-Swift-Protocols.md with new property pattern and examples

Motivation

This completes the work started in #563 which enforced throws(JSException) on protocol methods. Properties now follow the same pattern, fully addressing the inconsistency between import and export sides.

Notes

While working on this, I realized that removing the exception check condition in ImportTS.swift would break the current closure implementation - non-throwing closures would fail to compile.
Should we consider enforcing throws(JSException) on all closures as well? It makes sense given they're calling into JavaScript which can always throw. I'd prefer to tackle that in a separate follow-up PR.

[kateinoigakukun]

Should we consider enforcing throws(JSException) on all closures as well? It makes sense given they're calling into JavaScript which can always throw. I'd prefer to tackle that in a separate follow-up PR.

@krodak I'm tackling on it on my local branch, let's leave it as is for now.

[krodak]

After chat with @kateinoigakukun we agreed to not pursue throws(JSException) alignment for @JS protocol right now.

This PR (properties) and #563 (methods) were implemented to address consistency feedback from #560. After seeing the full picture - especially the setter method pattern for properties and questions about closures - we think the added complexity isn't worth it at this stage.

For current use cases, the simpler non-throwing protocol API works fine.
So I'll

• Close this PR
• Revert BridgeJS: Enforce throws(JSException) on @JS protocol methods #563

We can revisit alignment later if needed, now with implementation there is an understanding what it would actually take in user-facing interface, so gonna be easier to decide later on.