To formalize they are now XML-compliant (with some asterisks.)
Also to help syntax highlighters work on them to make their content more
readable.
Also:
- Delete empty comment decorations.
- GHA/checksrc: simplify XML check.
- runtests: fail to load test data with XML prolog missing.
Follow-up to bfe6eb1c06#19927
Follow-up to 87ba80a6dfCloses#19946
They were never officially allowed and slipped in only due to sloppy
parsing. Spaces (ascii 32) should be correctly encoded (to %20) before
being part of a URL.
The new flag bit CURLU_ALLOW_SPACE when a full URL is set, makes libcurl
allow spaces.
Updated test 1560 to verify.
Closes#7073