Add `proc-macro-server` command #7502

Job	Run time
build test linux x86-64	4m 20s
check-rust	3m 46s
build test windows x86-64	9m 11s
check-website	10s
scarb-metadata compatibility check	50s
doc tests	3m 18s
test linux x86-64 1/8	15m 52s
test linux x86-64 2/8	17m 18s
test linux x86-64 3/8	14m 36s
test linux x86-64 4/8	13m 19s
test linux x86-64 5/8	11m 36s
test linux x86-64 6/8	9m 49s
test linux x86-64 7/8	9m 45s
test linux x86-64 8/8	10m 45s
test windows x86-64 1/8	14m 58s
test windows x86-64 2/8	15m 25s
test windows x86-64 3/8	13m 47s
test windows x86-64 4/8	12m 27s
test windows x86-64 5/8	11m 56s
test windows x86-64 6/8	8m 53s
test windows x86-64 7/8	8m 53s
test windows x86-64 8/8	10m 5s
	3h 40m 59s

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