Make vroom::problems() work more like readr::problems()

[jennybc]

Seems like vroom::problems() could also consult .Last.value in the case of a missing primary input, as readr::problems() does.

https://github.com/tidyverse/readr/blob/5ac729aa9a70fef297a634d2332ff8ff1af874fb/R/problems.R#L24-L45

Seems like there should be more assessment of whether the input was explicitly provided or not. I think you'd want a higher level of skepticism / strictness for implicit input .Last.value than for explicitly passed input.

There will be several matters to think through here, around the co-existence and relationship between readr::problems() and vroom::problems().

[sbearrows]

This was meant to be closed with #446