R/extract_var_JSDM.R
extract_var_JSDM.RdExtract layers and create power wanted of each variable
stars object. output of "read_stars" of "stars" library with layer's names.
a character vector. of layer's name needed
int vector same length then `variables_names` . maximal power needed for each variable
boolean vector same length then `variables_names` . scale variables and its power
stars object with only variables and power asked.