BridgeJS: add runtime coverage for `public @JS struct` #2278

Job	Run time
build-examples	26m 12s
format	34s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	2m 57s
check-bridgejs-generated	2m 47s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 3s
Build for native target (macos-15, Xcode_16.4)	3m 58s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	17m 27s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	14m 1s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	13m 20s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	12m 57s
deploy-examples	0s
	1h 37m 16s

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