BridgeJS: Fix protocol existential lowering in Swift-to-JS direction #2468

Job	Run time
build-examples	7m 21s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 5s
prettier	10s
Build for native target (macos-15, Xcode_16.4)	2m 14s
format	33s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	2m 40s
check-bridgejs-generated	2m 35s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	2m 41s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	3m 2s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	2m 26s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	2m 40s
deploy-examples	1s
	29m 28s

Provide feedback