BridgeJS: Fix protocol existential lowering in Swift-to-JS direction #2469

Job	Run time
prettier	9s
build-examples	19m 41s
format	31s
check-bridgejs-generated	2m 52s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 2s
Build for native target (macos-15, Xcode_16.4)	2m 50s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	12m 51s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	3m 2s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	12m 45s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	17m 14s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	13m 56s
deploy-examples	0s
	1h 28m 53s

Provide feedback