[HttpFoundation] Fix parsing hosts and schemes in URLs

[nicolas-grekas]

Q	A
Branch?	6.4
Bug fix?	yes
New feature?	no
Deprecations?	no
Issues	-
License	MIT

This PR implements stricter parsing of URL hosts and schemes.
It hardens the codebase by making our interpretation or URLs closer to the spec.
This should help close potential semantic gaps between different layers of infrastructure.
The robustness principle is dead.

This topic has been raised by @zer0yu @P3ngu1nW @9vvert - thanks to them!

[9vvert]

Thanks for all your hard work on fixing this issue!
By the way, could you please assign a CVE for this vulnerability? Your assistance would be highly appreciated.
(if possible, the contributors are as follows:
Enze Wang
Jingcheng Yang
Zehui Miao
Jianjun Chen
)

[OskarStark]

AFAIK this is not a security vulnerability, otherwise it would be merged in 5.4 as well.

[9vvert]

Well. Still thank you for your time to fix it ! : )