Add tab-completion support to PEX repls. #2402

Job	Run time
Check GitHub Organization	1s
tox -e py312-pip23_3_2	17m 45s
./dtox.sh -e py27-pip20	12m 25s
tox -e py312-pip23_3_2-integration	38m 5s
tox -e format-check,lint-check,typecheck,vendor-check,package	4m 40s
./dtox.sh -e py35-pip20	13m 32s
./dtox.sh -e py311-pip20	15m 32s
./dtox.sh -e py311-pip22_3_1	16m 24s
./dtox.sh -e py311-pip23_1_2	15m 37s
./dtox.sh -e py312-pip23_3_2	15m 1s
./dtox.sh -e py313-pip24_0	15m 8s
./dtox.sh -e pypy310-pip20	25m 12s
./dtox.sh -e pypy310-pip22_3_1	25m 26s
./dtox.sh -e pypy310-pip23_1_2	25m 49s
./dtox.sh -e py27-pip20-integration	21m 53s
./dtox.sh -e py37-pip22_3_1-integration	41m 24s
./dtox.sh -e py37-pip23_1_2-integration	40m 31s
./dtox.sh -e py311-pip20-integration	24m 45s
./dtox.sh -e py311-pip22_3_1-integration	28m 23s
./dtox.sh -e py311-pip23_1_2-integration	27m 43s
./dtox.sh -e py312-pip23_3_2-integration	37m 14s
./dtox.sh -e py313-pip24_0-integration	41m 31s
./dtox.sh -e pypy310-pip20-integration	44m 55s
./dtox.sh -e pypy310-pip22_3_1-integration	52m 17s
./dtox.sh -e pypy310-pip23_1_2-integration	52m 20s
Gather Final Status	0s
	10h 53m 33s

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