balancer: Move metrics recorder from BuildOptions to ClientConn #13835

Job	Run time
vet-proto	21s
tests (vet, 1.22)	1m 48s
tests (extras, 1.23)	2m 58s
tests (tests, 1.23)	4m 33s
tests (tests, 1.23, -race)	5m 59s
tests (tests, 1.23, 386)	5m 5s
tests (tests, 1.23, arm64)	5m 43s
tests (tests, 1.22)	3m 54s
tests (tests, 1.23, -race, GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true)	6m 9s
	36m 30s

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