Nested elements generate duplicated css classes

[vladshcherbin]

Describe the bug
Nested selectors produce duplicated classes, e.g.: div.svelte-1aake2h.svelte-1aake2h

To Reproduce
https://svelte.dev/repl/7dbaf254c77a447bbba7a8eba33daf85?version=3.20.1

Expected behavior
In repl example, both div and p elements have duplicated classes. They should have 1 class as it makes css file larger with each element.

Information about your Svelte project:

• Svelte version 3.20.1
• Rollup

Severity
High. It has impact on all svelte projects.

[Conduitry]

Duplicate of #4374, the result of #4146, and not strictly a bug.

[vladshcherbin]

@Conduitry thanks, didn't succeed in finding similar issues 🕵️