TS2Swift: emit enums for string literal unions #2357

Job	Run time
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 18s
check-bridgejs-generated	2m 41s
Build for native target (macos-15, Xcode_16.4)	2m 13s
format	28s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	12m 36s
prettier	8s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	2m 58s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	17m 24s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	12m 48s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	12m 52s
build-examples	19m 50s
deploy-examples	0s
	1h 27m 16s

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