BridgeJS: Unify closure JS glue lift/lower

[kateinoigakukun]

Motivation

Refactoring to unlock #598

Changes

We had been having closure-specific lift/lower logic for JS glue codegen:

• closureLiftParameter
• closureLowerReturn
• closureLowerParameter
• closureLiftReturn

However, they are essentially the same as the regular lift/lower logic, so we should uniformly use them to reduce the cost of adding a new type support.

[Copilot]

Pull request overview

This PR refactors BridgeJS closure-related JS glue generation to reuse the shared lift/lower thunk builders, aiming to unify how Swift closures and JS callbacks are bridged.

Changes:

• Replaced bespoke closure parameter/return lift/lower code with ImportedThunkBuilder / ExportedThunkBuilder-based generation.
• Added hasDirectAccessToSwiftClass to IntrinsicJSFragment.PrintCodeContext to control whether generated JS can reference Swift heap object classes directly vs via _exports[...].
• Updated BridgeJSLink test snapshots for closure bridging (SwiftClosure*.js) to match the new generation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
Plugins/BridgeJS/Tests/BridgeJSToolTests/Snapshots/BridgeJSLinkTests/SwiftClosureImports.js	Snapshot update for closure import glue output.
Plugins/BridgeJS/Tests/BridgeJSToolTests/Snapshots/BridgeJSLinkTests/SwiftClosure.js	Snapshot update for closure glue output; exposes an optional Swift heap object construction scoping issue.
Plugins/BridgeJS/Sources/BridgeJSLink/JSGlueGen.swift	Introduces hasDirectAccessToSwiftClass and uses it when emitting Swift heap object construction in lift fragments.
Plugins/BridgeJS/Sources/BridgeJSLink/BridgeJSLink.swift	Refactors closure invoke/lower generation to use shared thunk builders; adjusts thunk builder function rendering API.

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