CSS string with escape newline ('\) breaks syntax hightlighting

[hibiyasleep]

Does this issue occur when all extensions are disabled?: Yes

• VS Code Version: 1.70.2
• OS Version: macOS 12.4

Steps to Reproduce:

1. Open empty document, set language to CSS.
2. write: body { content: 'a\ (newline here) b'; }
3. write some valid (or not) CSS code, all syntax highlighting gone.

when inspected, \ and all after is interpreted as constant.character.escape.newline.css.

css3 specs here: https://www.w3.org/TR/css-syntax-3/#consume-string-token
css21 specs here (with example of this case): https://www.w3.org/TR/CSS21/syndata.html#strings

[aeschli]

Duplicate of atom/language-css#181