BridgeJS: Move optional JSObject to stack ABI, enabling Optional<@JSClass> #2616

Job	Run time
format	31s
prettier	10s
build-examples	10m 58s
check-bridgejs-generated	2m 58s
Build for native target (macos-15, Xcode_16.4)	2m 19s
Test BridgeJS against Swift versions (swift:6.3, 603.0.0)	3m 10s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	3m 35s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	2m 56s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 15s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	3m 42s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	3m 5s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	2m 50s
deploy-examples	1s
	39m 30s

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