BridgeJS: fix: switch to direct TypeSyntax initialiser

[krodak]

This PR updates ExportSwift.lookupType to handle changes introduced in newer SwiftSyntax, that would result in failed compilation with errors like:

cannot convert value of type 'GenericArgumentSyntax.Argument' to expected argument type 'TypeSyntax'

This happened because in newer SwiftSyntax the .argument property of GenericArgumentSyntax no longer returns a TypeSyntax directly, but a new wrapper type (GenericArgumentSyntax.Argument).
I've just noticed this while working with other wasm32 Swift SDK with threads support, update approach should work properly for all sdk versions.

[Copilot]

Pull Request Overview

Fixes a compilation issue in BridgeJS by updating the handling of SwiftSyntax generic arguments to use direct TypeSyntax initializers instead of accessing the .argument property directly. This addresses breaking changes in newer SwiftSyntax versions where the argument property returns a wrapper type instead of TypeSyntax.

• Updates generic argument handling to use TypeSyntax initializer for compatibility
• Fixes two instances in the lookupType method for both identifier and member type handling

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[kateinoigakukun]

Could you add a runtime test case to cover the case to keep it compiled?

[kateinoigakukun]

Sorry, I was confused. Given that it's an issue at the compile-time of BridgeJSCore, we don't need a runtime test case 🙇