fix: pop drive-letter lookalike segment for non-file schemes (#2794)

[pasmud]

Fixes #2794: new URL('..', 'abc://x/y/z/C:/') must resolve to abc://x/y/z/ but rust-url refuses to pop the trailing C: segment.

Root cause

rust-url 2.5.8's last_slash_can_be_removed applies the Windows-drive-letter exemption to every scheme when shortening a path with .., but per the WHATWG URL Standard that exemption only applies to file:. For any other scheme a C:/C| segment is ordinary and must be popped. The upstream fix (servo/rust-url#1138) is open but unmerged, so this adds an in-repo workaround.

Change

• src/html5ever/url.rs: new fix_drive_letter_join helper, called from all four join/resolve FFI entry points (url_parse_with_base, url_join, url_resolve_without_encoding, url_resolve_with_encoding). When the base path ends with a drive-letter lookalike segment (/X:/ or /X|/) on a non-file scheme and the relative input starts with .., it pops that segment from the joined URL.
• src/browser/URL.zig: Zig test for the resolve path covering the WPT case plus the http variant, the C| form, control segments, the no-trailing-slash case, and the file: guard.

Verification

• cargo test --lib in src/html5ever: 4/4 pass (join cases, file guard, parse-with-base path, lookalike matcher).
• zig fmt --check src/browser/URL.zig: clean.
• Full zig build test could not run in this sandbox: the build fetches V8 + dependencies from GitHub, which the sandbox proxy/DNS rejects (HttpConnectionClosing/TemporaryNameServerFailure). The behavior was verified end-to-end via the Rust crate tests plus a raw probe of rust-url (abc://x/y/z/C:/ + .. returns the buggy abc://x/y/z/C:/ before the fix, abc://x/y/z/ after).

[krichprollsch]

Thanks for your contribution.
I saw there is also an open PR on rust-url to fix the issue: servo/rust-url#1138
What about waiting for the merge?

[nikneym]

Hi & thank you for your contribution. We were actually hoping if servo/rust-url#1138 be merged so I'd like to keep this open for a little more and take action if it won't be fixed in the upstream.