Refactor resolver to nudge to adding row names to columns + improve error message + refactor tests

[olivroy]

Summary

In short the stub created when rownames are not present prevents us from using row names.

I noticed that a way to find out this is to notice that all items are NA, it means they don't exist.

Instead of showing which row names couldn't be resolved, nudge towards adding row names to the gt table instead.

I also took advantage of this PR to remove a duplicate test in test-tab_style.R and merge the tests for output + deprecated arguments.

I have to say that I didn't know the existence of tab_row_group() before. I think this function should be deprecated in favour of a case_match() syntax.

# not the best name, but similar syntax as another one.
stub_row_group <- function(..., .default) {
}
exibble |>
  gt(rowname_col = ) |>
  stub_rows_group(
     c(1, 2) ~ "grp1",
    .default = "Other"
  )

Honestly, I would have had trouble finding tab_options(row_group.default_label) without trying the others_label first and getting the nudge there. (It is documented, but still feels like not the best design). Oh, this is #729!

Related GitHub Issues and PRs

fix #1535

Checklist

• I understand and agree to the Code of Conduct.
• I have listed any major changes in the NEWS.
• I have added testthat unit tests to tests/testthat for any new functionality.

[rich-iannone]

LGTM!