ggMarginal can’t handle Date axes

```r
library(ggExtra)
data(airquality)
airquality$Date <- with(airquality, as.Date(sprintf('1973-%02d-%02d', Month, Day)))

p <- ggplot(airquality, aes(Date, Temp)) + geom_point()
print(ggMarginal(data = airquality, x = 'Date', y = 'Temp')) # works
print(ggMarginal(p, airquality, 'Date')) # doesn’t
```

the second one throws:

```r
Error: Invalid input: date_trans works with objects of class Date only
Traceback:

1. print(ggMarginal(p, airquality, "Date"))
2. ggMarginal(p, airquality, "Date")
3. ggplot2::ggplot_build(top)
4. lapply(data, scales_transform_df, scales = scales)
5. FUN(X[[i]], ...)
6. unlist(lapply(scales$scales, function(s) s$transform_df(df = df)),
. recursive = FALSE)
7. lapply(scales$scales, function(s) s$transform_df(df = df))
8. FUN(X[[i]], ...)
9. s$transform_df(df = df)
10. f(..., self = self)
11. lapply(df[aesthetics], self$transform)
12. FUN(X[[i]], ...)
13. f(..., self = self)
14. self$trans$transform(x)
15. stop("Invalid input: date_trans works with objects of class Date only",
. call. = FALSE)
```

Start by running the supplied airquality reproduction and compare the two ggMarginal calls, following the failing path through ggMarginal and ggplot2::ggplot_build. Done means the second call accepts the Date axis without the date_trans error and preserves the marginal plot behavior.

Written by the indexing model from the issue text.