Add `proc-macro-server` command #7446

Job	Run time
build test linux x86-64	1s
build test linux x86-64	4m 25s
build test windows x86-64	12m 13s
build test windows x86-64	12m 13s
check-rust	1s
check-rust	4m 6s
check-website	1s
check-website	11s
scarb-metadata compatibility check	1s
scarb-metadata compatibility check	46s
doc tests	1s
doc tests	3m 11s
test ${{ matrix.platform.name }} ${{ matrix.partition }}/8	1s
test linux x86-64 1/8	15m 54s
test linux x86-64 2/8	16m 49s
test linux x86-64 3/8	14m 57s
test linux x86-64 4/8	12m 43s
test linux x86-64 5/8	12m 9s
test linux x86-64 6/8	9m 17s
test linux x86-64 7/8	9m 25s
test linux x86-64 8/8	10m 34s
test windows x86-64 1/8	13m 50s
test windows x86-64 2/8	16m 10s
test windows x86-64 3/8	13m 32s
test windows x86-64 4/8	13m 10s
test windows x86-64 5/8	11m 34s
test windows x86-64 6/8	9m 0s
test windows x86-64 7/8	8m 7s
test windows x86-64 8/8	10m 9s
	3h 54m 31s

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