fix: body styling with columns = everything() can miss columns when a multi-column stub is present

[rich-iannone]

This PR fixes an issue where a table that has multiple stub columns, the styling is not applied to all columns even though columns = everything() is used in cells_body(). With this fix, the following gt code now works correctly:

library(gt)
library(dplyr)

gt::exibble |> 
  select(char, fctr, date, row) |> 
  gt(rowname_col = c("char", "fctr" )) |> 
  tab_style(
    style = cell_borders(
      sides = c("top","bottom"),
      color = "transparent"
    ),
    locations= list(
      cells_body(
        columns = tidyselect::everything(),
        rows = tidyselect::everything()
      ),
      cells_stub(),
      cells_row_groups()
    )
  ) 

Fixes: #2094