Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.
This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.
Closes#8869
- the data needs to be "line-based" anyway since it's also passed to the
debug callback/application
- it makes infof() work like failf() and consistency is good
- there's an assert that triggers on newlines in the format string
- Also removes a few instances of "..."
- Removes the code that would append "..." to the end of the data *iff*
it was truncated in infof()
Closes#7357
