xds: generic xds client resource watching e2e #14879

Job	Run time
vet-proto	37s
vet-proto	37s
tests (vet, 1.23)	2m 23s
tests (vet, 1.23)	2m 23s
tests (extras, 1.24)	3m 3s
tests (extras, 1.24)	3m 3s
tests (tests, 1.24)	4m 3s
tests (tests, 1.24)	4m 18s
tests (tests, 1.24, -race)	5m 9s
tests (tests, 1.24, -race)	5m 21s
tests (tests, 1.24, 386)	4m 25s
tests (tests, 1.24, 386)	4m 25s
tests (tests, 1.24, arm64)	6m 16s
tests (tests, 1.24, arm64)	6m 12s
tests (tests, 1.23)	3m 42s
tests (tests, 1.23)	3m 46s
tests (tests, 1.24, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=false)	5m 26s
tests (tests, 1.24, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=false)	5m 31s
	1h 10m 40s

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