[nesting] Move CSSNestedDeclarations/whitespace tests to separate file
This is just to move the tests out of the Interop 2024 set.
Change-Id: I2f01f97a29b53584daa6591b48bc33922f0c5ded
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5920495
Reviewed-by: Rune Lillesveen futhark@chromium.org
Commit-Queue: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1366135}