Added the tag enun name to the profiling marks.

For example, whereas previously we'd have

GRPC_LAT_PROF 1986206380734.095703 0x7f0b4bff7700 { 200 (nil) src/core/iomgr/tcp_posix.c 337

now we have:

GRPC_LAT_PROF 1986206380734.095703 0x7f0b4bff7700 { 200(GRPC_PTAG_HANDLE_READ) (nil) src/core/iomgr/tcp_posix.c 337

Note the literal enum name in parenthesis following the tag int value.