BridgeJS: support imports of JS `Promise` as `async` Swift #2518

Job	Run time
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	26s
build-examples	53s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	54s
prettier	18s
check-bridgejs-generated	45s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	45s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	55s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	1m 6s
Build for native target (macos-15, Xcode_16.4)	56s
format	37s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	51s
deploy-examples	1s
	8m 27s

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