BridgeJS: Fix protocol existential lowering in Swift-to-JS direction #2466

Job	Run time
Build for native target (macos-15, Xcode_16.4)	2m 1s
prettier	11s
format	32s
check-bridgejs-generated	2m 34s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	8m 4s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	8m 4s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 13s
build-examples	8m 2s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	8m 5s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	3m 3s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	8m 4s
deploy-examples	1s
	51m 54s

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