[NFC] BridgeJS: Codegen code organisation and minor cleanups #1849

Job	Run time
Build for native target (macos-15, Xcode_16.4)	38s
format	33s
check-bridgejs-generated	5m 19s
build-examples	11m 33s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	6m 25s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	5m 42s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	5m 31s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.0.2-release/ubuntu2204/swift-6.0...	4m 40s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	5m 42s
deploy-examples	0s
	46m 3s

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