fix: correct VendorPrefix for ::-ms-input-placeholder pseudo-element

[Noethix55555]

src/selector.rs line 294 maps the ::-ms-input-placeholder pseudo-element to VendorPrefix::Moz instead of VendorPrefix::Ms — a copy-paste error from the line above (-moz-placeholder).

The serializer at line 1244 branches on the stored prefix:

Placeholder(prefix) => {
    let vp = write_prefix!(prefix);
    if vp == VendorPrefix::WebKit || vp == VendorPrefix::Ms {
        dest.write_str("input-placeholder")
    } else {
        dest.write_str("placeholder")
    }
}

Because the stored prefix is Moz, the wrong branch fires: the -moz- vendor prefix is written, and placeholder (not input-placeholder) is appended. Any stylesheet that already contains ::-ms-input-placeholder is silently rewritten to ::-moz-placeholder — a completely different selector.

Repro:

input::-ms-input-placeholder { color: red; }

Before this fix, lightningcss outputs:

input::-moz-placeholder{color:red}

After this fix:

input::-ms-input-placeholder{color:red}

Fix: change VendorPrefix::Moz to VendorPrefix::Ms on line 294. Three round-trip minify_test assertions are added to prevent regression.