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
If the QLOGDIR environment variable is set, enable qlogging.
... and create Curl_qlogdir() in the new generic vquic/vquic.c file for
QUIC functions that are backend independent.
Closes#5353
