Extract {or,origin}_circuit_t into their own headers

src/or/circpathbias.c

src/or/circuitbuild.c

src/or/circuitlist.c

src/or/circuitlist.h

src/or/circuitmux.c

src/or/circuitstats.c

src/or/circuituse.c

src/or/command.c

src/or/connection_edge.c

src/or/control.c

src/or/cpuworker.c

src/or/directory.h

src/or/dns.c

src/or/entrynodes.c

src/or/hs_cell.c

src/or/hs_circuit.c

src/or/hs_circuitmap.c

src/or/hs_client.c

src/or/hs_common.c

src/or/hs_intropoint.c