BridgeJS: add init(unsafelyCopying:) for @JS structs #1974

Job	Run time
Build for native target (macos-15, Xcode_16.4)	3m 17s
format	37s
check-bridgejs-generated	2m 38s
build-examples	43m 3s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	12m 3s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	17m 42s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	13m 8s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	13m 53s
deploy-examples	0s
	1h 46m 21s

Provide feedback