BridgeJS: fix codegen for async + throws exported methods #2446

Job	Run time
prettier	10s
Build for native target (macos-15, Xcode_16.4)	2m 32s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 24s
format	36s
build-examples	19m 31s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	3m 14s
check-bridgejs-generated	2m 29s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	17m 4s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	13m 45s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	12m 42s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	13m 5s
deploy-examples	0s
	1h 28m 32s

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