[css-nesting] Add CSSNestedDeclarations support for insertRule
As part of the overall CSSNestedDeclarations change,
the "insert a CSS rule" algorithm [1] now includes a step to retry
parsing of a failed rule as a CSSNestedDeclarations rule [1].
This CL implements that change.
[1] https://drafts.csswg.org/cssom/#insert-a-css-rule
Bug: 343463516
Change-Id: I4b81da404a26cc036a3fcf0aebdbef0775eac0a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5826512
Reviewed-by: Steinar H Gunderson sesse@chromium.org
Commit-Queue: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1349786}