Augment Abort & co.; add rlang condition tutorial, helpers

[brookslogan]

This is a draft. The additional Abort&co. features still need to have testthat tests, and to be used throughout the package.

Motivation: we "use" rlang conditions, but

• don't use any of its formatting, error class name, and error object field-setting features.
• this breaks the options(error=recover) debugging workflow in at least some R versions
• many users may be unaware of some of the features of rlang conditions from just following the prompts to rlang::last_error() and rlang::last_trace()

We want to help users get accustomed to rlang conditions, and take advantage of more of its features; building on Abort and Warn seems like a good way.

Changes so far:

• Add Inform, similar to Abort and Warn
• Add class_suffix, display_subfields, more_subfields, and call to
  Abort, Warn, Inform
• On first raised condition, provide a tutorial on rlang conditions to help
  users with compatibility issues and potentially-unknown features
• Improve condition traces via call default
• Improve condition message line wrapping, compatibility with messages with
  bullet points, etc.

To complement the tutorial, some convenience functions for working with global calling handlers, as well as some handler functions, are provided.

[brookslogan]

Roxygen templates provide a different way to execute dynamic code with <%= ...... %>. Might provide a way around the line wrap fighting. (Here and in other template file, and maybe also in other non-template places where dynamic R code is used that could be turned into templates.)

[brookslogan]

Might need @noRd here and in other internal helper functions. Not the handler ones though, as they will be referenced by the tutorial.

[brookslogan]

vs. @keywords internal?

[brookslogan]

• Printing of more debug fields might need to be done via encodeString. this doesn't do the conditional backtick quoting I initially thought it was supposed to do (too hastily read the first part of the docs). Perhaps there is some sort of encoding correctness to think about, but it'd probably be across the entire package as best practices rather than something specific here.

[brookslogan]

• For migration from existing Abort etc., should allow class parameter as an alternative to class_prefix parameter.
• Resolve merge conflicts.
• To prevent strange tutorial placement especially with some warning spam, consider only showing tutorial by default for Abort.
• Add tests.
• Use throughout package + add issue to use in code developed in parallel with these changes.
• Allow debug info display function to be customizable rather than hard-coded as str.
• Consider pointing to and using rlang::try_fetch rather than withCallingHandlers and/or tryCatch.
• Consider moving from templates to @eval of functions returning roxygen tags. See here.
• Use cat_varnames (under dev in lcb/grouped_epi_archive) for printing subfield names
• Check usage of nchar: check whether/which calls should use type="width"
• Check naming of check_* functions / change them to make them idiomatic
• Go ahead and move to cli_* or use_cli_format since we transitively import it anyway.