fix(supports): keep the vendor prefix on a feature query inside and/or

[oddharsh]

Fixes #710.

The @supports merge pass binds the unprefixed id over property_id, and then uses that binding for two more things: what it stores, and which prefix it merges in.

let property_id = property_id.with_prefix(VendorPrefix::None);   // shadows
let key = (property_id.clone(), value.clone());
if let Some(index) = seen_declarations.get(&key) {
    cur_property.add_prefix(property_id.prefix());               // always VendorPrefix::None
} else {
    seen_declarations.insert(key, conditions.len());
    conditions.push(SupportsCondition::Declaration { property_id, value });   // stored stripped
}

So a condition matching nothing already seen is pushed with its prefix gone, and (-webkit-box-orient: vertical) becomes (box-orient: vertical) — which no browser implements, so the block it guards silently never applies.

Using a separate binding for the match key fixes both symptoms. The unprefixed id is the key only; the condition keeps the prefix it was written with, and the merge branch adds the real prefix instead of None.

Why it reads as an inconsistency rather than a plain regression

A prefixed query survives when it stands alone, because that path pushes in_parens untouched. It is only stripped as an operand of and / or. Measured on 1.33.0 before this change:

condition	alone	inside (display:flex) or …
(-webkit-box-orient:vertical)	preserved	(box-orient:vertical)
(-webkit-backdrop-filter:blur(1px))	preserved	(backdrop-filter:blur(1px))
(-moz-appearance:none)	preserved	(appearance:none)

Worth knowing for anyone triaging this: reducing a report to a single condition to check whether it still reproduces answers no on a build that is still broken.

Why the existing tests did not catch it

Every assertion added with the merge feature in 6bd2761 sets Browsers targets, and the prefixing pass then re-adds what the merge dropped. The regression tests here deliberately set none, and they use minify_test rather than prefix_test for that reason.

Verification

Before and after, same input, minify: true, no targets:

BEFORE   @supports (display:flex) and (box-orient:vertical){a{color:red}}
AFTER    @supports (display:flex) and ((-webkit-box-orient:vertical)){a{color:red}}

• 120/120 lib tests pass, including the merge assertions from 6bd2761
• the three added tests fail without the fix, printing the stripped form, and pass with it
• cargo fmt leaves both changed files untouched (it does reformat bundler.rs, selector.rs and an unrelated lib.rs line under current rustfmt; those are deliberately not included here)