`,` escape breaks svelte scoping

[Alexander Niebuhr]

Using a class like grid-cols-[repeat(6,1fr)], unocss will escape , in the selector with \2c. This works as a style, but it will not work with svelte's check for unused styles in scope mode.
Therefore the style is removed on build time, leading to missing style.

Just using the \, to escape the comma (as seen in the example) will make the style work and svelte actually understand that the style is used.

Actual Output:
https://stackblitz.com/edit/web-platform-1asmuc?file=styles.css

Expected Output:
https://stackblitz.com/edit/web-platform-akerk4?file=styles.css

[Anthony Fu]

The escape function was copied from somewhere else. If you can make sure the new escape works on browsers, feel free to change the code and send a PR. Thanks.