Formatting: match CSS function names case-insensitively in safecss_fi…

[Anupkankale]

CSS function names are ASCII case-insensitive, so CALC(1px + 2px), URL(foo.jpg), and LINEAR-GRADIENT(red, blue) are all valid CSS. Every function-matching pattern in safecss_filter_attr() was case-sensitive, however, so valid declarations using anything other than all-lowercase function names were silently dropped.

Add the i modifier to the url(), gradient, and generic function patterns, and lowercase the value before the url( / -gradient( sniffing done for custom properties.

Only the function names are matched loosely; the grammar each pattern accepts is unchanged, so a mixed-case value is now held to exactly the same standard as its lowercase equivalent. Protocol checking in wp_kses_bad_protocol() was already case-insensitive, so URL() values are validated the same way url() values are.

Property names remain case-sensitive, which is a separate concern.

Fixes #65838. See #64974.

Trac ticket:

Use of AI Tools

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[irozum]

Nice fix — CSS function names genuinely are ASCII case-insensitive, so silently dropping CALC(...)/URL(...)/LINEAR-GRADIENT(...) while accepting the lowercase equivalents was a real (if minor) sanitizer bug, and this closes the gap without loosening the actual grammar each pattern accepts.

I checked out the branch and ran the affected suite (--filter Tests_Kses, 451 tests/1525 assertions, all green, including the new mixed-case data provider cases), plus composer lint:errors and phpstan on kses.php — both clean.

I traced the security-relevant path by hand: wp_kses_bad_protocol_once2() already lowercases the scheme before comparing against $allowed_protocols (kses.php:2057), so URL(JavaScript:...) is rejected exactly like url(javascript:...) — confirmed by the new test cases. And since only the function names get the /i modifier while each pattern's grammar is untouched, an unrecognized/malformed mixed-case function (e.g. EXPRESSION(...)) still leaves its ( in the test string and gets caught by the trailing [\\(&=}] check. Good call leaving property-name case-sensitivity (Text-transform) out of scope — that's a separate, more debatable question.

One small thing unrelated to the code: the PR body has "Fixes #65838" in prose but the template's "Trac ticket:" line is still empty, which is why the props bot flagged a missing Trac link — worth filling in the full https://core.trac.wordpress.org/ticket/65838 URL there so the linkage is picked up automatically.