Typo3 was relaying on the feature of base converter
functions silently removing invalid chars so, for example:
'U+00A0' => '00A0' => 160
Since php74, the existence of those invalid chars do produce
a deprecation warning, no matter the outcome continues being the same.
So, here, we are just converting that invalud 'U+' by '0x'
The explicit usage of the constants FILTER_FLAG_SCHEME_REQUIRED and
FILTER_FLAG_HOST_REQUIRED is now deprecated; both are implied for
FILTER_VALIDATE_URL anyway.
