Add input check functions using {cli}

[elipousson]

Adds helper functions for input checks for arc_open(), add_features(), update_features(), and add_item() including:

• check_dataframe
• check_url (w/ is_url)
• check_string
• check_crs_match
• check_add_item_args

Also adds inform_nin_feature() to reduce duplicative code between add_features() and update_features().

Also tries to make error and warning messages more consistent internally and consistent with the tidyverse style guide for error messages.

Checklist

• update NEWS.md
• documentation updated with devtools::document()
• devtools::check() passes locally

Changes

This adds the general helper functions listed above to utils.R and other functions as appropriate. I did not include updates to NEWS.md or any changes to documentation in this PR.

Follow up tasks

More consistent input checks should be implemented overall and URL checking could be improved to ensure input URL is consistent with the type of URL that could be a ArcGIS Server or ArcGIS Online URL.

[JosiahParry]

Using this as an opportunity to fix some issues with the readme.

[JosiahParry]

Sweeeeett! Thank you! I've simplified some code and made some adjustments where i saw fit. Thank you Veryyy much!

[elipousson]

Great! The pattern argument in check_url could also help functions error on invalid URLs. I think the URL patterns for ArcGIS REST servers and AGOL services are consistent enough to support those kind of checks.