Add VLOGs in key areas to enable easier debugging of collective execution.

To turn on logging for individual components, set the TF_CPP_VMODULE
environment variable to a comma-separated list of log levels.  e.g.
TF_CPP_VMODULE="a=1,b=2" would write all VLOGs upto level 1 for a.{h,cc} and
upto level 2 for b.{h,cc}.
PiperOrigin-RevId: 232751196