added emsdk and build script #339

Job	Run time
test-unix (ubuntu-20.04, static_build)	1m 18s
test-unix (ubuntu-20.04, shared_build)	2m 8s
test-unix (ubuntu-22.04, static_build)	1m 22s
test-unix (ubuntu-22.04, shared_build)	2m 18s
test-unix (macos-11, static_build)	4m 1s
test-unix (macos-11, shared_build)	4m 8s
test-unix (macos-12, static_build)	3m 31s
test-unix (macos-12, shared_build)	2m 41s
test-wasm (3.1.45)	13m 39s
test-win (windows-2019, static_build)	6m 46s
test-win (windows-2019, shared_build)	5m 1s
test-win (windows-2022, static_build)	5m 59s
test-win (windows-2022, shared_build)	3m 16s
	56m 8s

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