Loads precomputed correlation matrices for a single region.
Source:R/ctwas_region_cor.R
load_region_cor.RdIt loads precomputed correlation matrices for a single region.
It could load correlation matrices by region_id and
directory of correlation matrices cor_dir. Otherwise,
it loads correlation matrices by the
filenames (R_sg_file, R_sg_file, R_s_file)
if they are provided.