Internal function to get centered cp objects

Needed a function for this because we do it twice: once for regional RRs and once for BLUP

Usage

get_centered_cp(
  argvar,
  xcoef,
  xvcov,
  this_exp,
  x_b,
  global_cen,
  cen,
  exposure_is_factor
)

Arguments

exposure_is_factor