Support `--sh-boot` for `--layout {loose,packed}`. #3321

Job	Run time
Check GitHub Organization	1s
./dtox.sh -e py27-pip20	10m 8s
tox -e format-check,lint-check,typecheck,enum-check,vendor-check,package,docs	10m 29s
./dtox.sh -e py38-pip22_3_1	17m 0s
tox -e py313-pip24_3_1	17m 6s
./dtox.sh -e py311-pip23_3_2	16m 59s
tox -e py313-pip24_3_1-integration --shard 1/2	25m 26s
./dtox.sh -e py313-pip24_3_1	13m 35s
tox -e py313-pip24_3_1-integration --shard 2/2	28m 34s
./dtox.sh -e py314-pip24_3_1	13m 31s
./dtox.sh -e pypy310-pip24_3_1	25m 0s
./dtox.sh -e py27-pip20-integration	25m 0s
./dtox.sh -e py38-pip22_3_1-integration --shard 1/2	24m 59s
./dtox.sh -e py38-pip22_3_1-integration --shard 2/2	24m 59s
./dtox.sh -e py311-pip23_3_2-integration --shard 1/2	25m 1s
./dtox.sh -e py311-pip23_3_2-integration --shard 2/2	25m 0s
./dtox.sh -e py313-pip24_3_1-integration --shard 1/2	24m 30s
./dtox.sh -e py313-pip24_3_1-integration --shard 2/2	25m 0s
./dtox.sh -e py314-pip24_3_1-integration --shard 1/2	24m 44s
./dtox.sh -e py314-pip24_3_1-integration --shard 2/2	25m 1s
./dtox.sh -e pypy310-pip24_3_1-integration --shard 1/2	14m 25s
./dtox.sh -e pypy310-pip24_3_1-integration --shard 2/2	24m 59s
Gather Final Status	0s
	7h 21m 27s

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