Allocate token's content into an arena #7364

Job	Run time
build test linux x86-64	4m 7s
check-rust	3m 47s
check-website	10s
scarb-metadata compatibility check	53s
build test windows x86-64	8m 16s
doc tests	3m 4s
test linux x86-64 1/8	16m 46s
test linux x86-64 2/8	18m 2s
test linux x86-64 3/8	16m 5s
test linux x86-64 4/8	13m 43s
test linux x86-64 5/8	13m 30s
test linux x86-64 6/8	10m 24s
test linux x86-64 7/8	10m 21s
test linux x86-64 8/8	11m 2s
test windows x86-64 1/8	14m 21s
test windows x86-64 2/8	17m 51s
test windows x86-64 3/8	13m 49s
test windows x86-64 4/8	13m 4s
test windows x86-64 5/8	11m 19s
test windows x86-64 6/8	9m 33s
test windows x86-64 7/8	9m 3s
test windows x86-64 8/8	11m 4s
	3h 50m 14s

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