Don't always convert dppx unit to x unit in resolution media queries

[yisibl]

css-values-4 adds x as an alias for dppx unit, but not every browser in media queries supports x unit. So I think it would be better to add a fallback for x unit.

x unit support in: Chrome 68+, Edge 79+, Opera 55+, Safari 16+, Firefox 62+

Input

@media (resolution: 1dppx) { /* or resolution: 1x */
    body {
       background: red;
    }
}

Output

@media (resolution: 1x) {
    body {
       background: red;
    }
}

Expected

@media (resolution: 1dppx), (resolution: 1x) {
    body {
       background: red;
    }
}

Minify

When compressing, if the configured browser version does not support x unit, only dppx will be retained.

@media (resolution: 1dppx) {
    body {
       background: red;
    }
}

See also: postcss/autoprefixer#1468

[devongovett]

One place where this doesn't apply is image-set(), where 1x/2x etc. are supported much earlier than other resolutions.