This function is used internally by plotting helpers such as
.plot_bars() and .plot_heatmap() to avoid hard-coding the
label column name.
.get_numbers_col(numbers, col = ".values")A character string with the column name to be used for plotting numbers,
or NULL if no numbers should be displayed.
The numbers parameter passed to the high-level plotting.
Name of the column containing the prepared label values. Defaults to ".values".