blockstore: store first received coding shred index in ErasureMeta (#… #83

Job	Run time
ios (macos-11, aarch64-apple-ios)	7m 12s
android (ubuntu-20.04, x86_64-linux-android)	3m 1s
ios (macos-11, x86_64-apple-ios)	7m 14s
android (ubuntu-20.04, aarch64-linux-android)	3m 5s
ios (macos-11, aarch64-apple-darwin)	7m 40s
android (ubuntu-20.04, i686-linux-android)	3m 8s
ios (macos-11, x86_64-apple-darwin)	7m 31s
android (ubuntu-20.04, armv7-linux-androideabi)	3m 14s
error_reporting	0s
	42m 5s

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