cleanup: Modernize C++ struct/enum/union declarations #4835

Job	Run time
build-libs-emscripten 🧐	3m 49s
build-libs-linux-amd64 😁 (system_deps)	5m 18s
build-libs-linux-amd64-asan 🧐	8m 19s
build-libs-linux-amd64-static 🎃	22m 27s
build-libs-linux-amd64 😁 (bundled_deps)	16m 50s
build-libs-linux-amd64 😁 (system_deps_w_chisels)	5m 14s
build-shared-libs-linux-amd64 🧐	3m 44s
build-libs-others-amd64 😨 (windows-latest)	7m 56s
build-libs-linux-amd64 😁 (system_deps_minimal)	3m 38s
build-libs-others-amd64 😨 (macos-latest)	6m 55s
build-libs-linux-arm64 😁 (system_deps)	5m 42s
build-shared-libs-macos-amd64 😨	4m 39s
build-libs-linux-arm64 😁 (bundled_deps)	17m 11s
test-libs-static (bundled_deps)	14m 47s
build-libs-linux-arm64 😁 (system_deps_w_chisels)	5m 51s
build-libs-linux-arm64 😁 (system_deps_minimal)	4m 7s
run-e2e-tests-amd64 (system_deps)	8m 36s
run-e2e-tests-amd64 (bundled_deps)	19m 51s
run-e2e-tests-amd64 (system_deps_w_chisels)	8m 53s
run-e2e-tests-amd64 (asan)	20m 57s
	3h 14m 44s

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