BridgeJS: Adjust for the latest top-level requirement for `@_extern(wasm)` #1812

Job	Run time
Build for native target (macos-15, Xcode_16.4)	1m 51s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	5m 26s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.0.2-release/ubuntu2204/swift-6.0...	5m 4s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	5m 28s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	6m 17s
format	33s
build-examples	11m 37s
check-bridgejs-generated	5m 32s
deploy-examples	-1s
	41m 47s

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