[css] support IE repeat syntax

[miaomiaoji]

the code :

  .wrapper {
            display: -ms-grid;
            display: grid;
            -ms-grid-columns: (1fr)[4];
            grid-template-columns: repeat(4, 1fr);
        }

the forth line has a special value'(1fr)[4]'，it triggers error(s)

"code": "css-lbracketexpected",
"message": "] expected",

even though,it's not fatal,the value above equals 1fr 1fr 1fr 1fr,and does not trigger error.
the code is auto created by a extension(autoprefixer),and it's normal behave in browser.
it just show error things in vscode,I don't know Whether this problem can be fixed?

[aeschli]

https://css-tricks.com/css-grid-in-ie-debunking-common-ie-grid-misconceptions/#article-header-id-1