add support for "Svelte: Show Compiled CSS"

[kwangure]

Is your feature request related to a problem? Please describe. The Svelte: Show Compiled Code feature is helpful for compiling JS code, but there seems to be no CSS equivalent. Showing compiled CSS code is particularly helpful when dealing with preprocessors that manipulate CSS.

Describe the solution you'd like This is a request for a "Svelte: Show Compiled CSS" feature that outputs the CSS of a file after preprocessing.

Describe alternatives you've considered My current workflow involves toggling sourcemaps back and forth or running npm run build and finding the CSS bundle.