feat: Allow reqsign to be used in wasm (#397) #847

Job	Run time
check	41s
build (ubuntu-latest)	34s
build_under_wasm	33s
build (macos-11)	1m 20s
build (windows-latest)	2m 45s
test_gcs_web_identify	1m 7s
build_all_features (ubuntu-latest)	43s
test_tencent_cloud_web_identify	1m 8s
build_all_features (macos-11)	1m 31s
unit	1m 10s
build_all_features (windows-latest)	2m 24s
test_aws_web_identity	1m 5s
	15m 1s

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