BridgeJS: Perf-tune `SwiftToSkeleton` by avoiding unnecessary Syntax node allocation #2121

Job	Run time
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	2m 58s
check-bridgejs-generated	2m 38s
build-examples	17m 59s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	2m 52s
format	31s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	16m 37s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	13m 9s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	12m 49s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	13m 25s
Build for native target (macos-15, Xcode_16.4)	2m 57s
deploy-examples	0s
	1h 25m 55s

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