Support re-exported contracts in build-external #8246

Job	Run time
scarb-metadata compatibility check	51s
check-rust	3m 46s
build test linux x86-64	4m 15s
check-website	13s
build test windows x86-64	9m 8s
doc tests	3m 29s
test linux x86-64 1/8	21m 28s
test linux x86-64 2/8	25m 6s
test linux x86-64 3/8	20m 27s
test linux x86-64 4/8	18m 16s
test linux x86-64 5/8	15m 13s
test linux x86-64 6/8	16m 12s
test linux x86-64 7/8	12m 24s
test linux x86-64 8/8	14m 53s
test windows x86-64 1/8	20m 2s
test windows x86-64 2/8	23m 3s
test windows x86-64 3/8	20m 31s
test windows x86-64 4/8	15m 56s
test windows x86-64 5/8	16m 40s
test windows x86-64 6/8	14m 30s
test windows x86-64 7/8	11m 36s
test windows x86-64 8/8	14m 44s
	5h 2m 43s

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