Change the data arg to .data to avoid partial matching issues

[rich-iannone]

In functions like cols_label(), having a column name close to data may result in a partial matching error. Here's a reproducible example of the error:

tribble(
  ~a , ~d ,
  1, 4,
  5, 8
) %>% 
  gt() %>% 
  cols_label(
    a = "label a",
    d = "label d"
  )

#> Error: The object to `data` is not a `gt_tbl` object.

This can be solved by changing the argument name to .data. For consistency, all instances of data as argument names in exported functions were changed to .data.

On the user side, there should hopefully be little disruption as all examples and ways of using the gt API don't use the argument name data (either via piping or through implicit use of data when just using gt()).

Fixes: #715

[jcheng5]

Let's check lapply(as.list(as.environment("package:gt")), args) and see what other functions have unbounded possibilities for ...

[rich-iannone]

Let's check lapply(as.list(as.environment("package:gt")), args) and see what other functions have unbounded possibilities for ...

The cols_label() and cols_width() functions both have ... but the only other non-data arg for both is .list. So no other issues there.

The summary_rows() and grand_summary_rows() functions also have ... but after looking at the function signatures of all the fmt_*() functions, none except for fmt_missing() (which you wouldn't use in summary_rows() or grand_summary_rows()) have arguments that collide with the summary functions. Quite a bit of testing was done to check that partial matching doesn't lead you to a strange error in the summary functions.

[rich-iannone]

Changes have now been made to limit the data -> .data arg renaming to only the cols_label() and cols_width() functions.