[NFC] BridgeJS: Codegen code organisation and minor cleanups #1851

Job	Run time
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.0.2-release/ubuntu2204/swift-6.0...	4m 47s
format	34s
check-bridgejs-generated	5m 38s
build-examples	11m 40s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	5m 48s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	5m 50s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	7m 5s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	5m 43s
Build for native target (macos-15, Xcode_16.4)	42s
deploy-examples	0s
	47m 47s

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