Allow stacked bars for data containing negative y-values in `type_barplot()`

When plotting a stacked bar chart with negative values, tinyplot doesn't stack them the way ggplot2 does for example. Currently for data that contains negative y-values the following warning is shown:

Warning message:
In settings$type_data(settings, ...) :
  'beside' must be TRUE if there are negative 'y' values

and the bars are put beside. For some data it would make sense to show the bars stacked even if some values are negative (e.g. balances like below):

rm(list = ls())

library(tinyplot)
library(worldbank)
library(ggplot2)

df <- wb_data(
  indicator = c("BN.GSR.GNFS.CD", "BN.GSR.FCTY.CD", "BN.TRF.CURR.CD"),
  country = "US"
)

# tinyplot
plt(
  value ~ date | indicator_id,
  data = df,
  type = "barplot"
)

# ggplot2
ggplot(df, aes(fill=indicator_id, y=value, x=date)) + 
  geom_bar(position="stack", stat="identity")

Start at type_barplot() and the settings$type_data() path indicated by the warning, then reproduce the stacked-bar example with negative y-values. Trace how negative values force beside mode and make the result retain stacked behavior without the warning, matching the ggplot2 example.