[container-queries] Enforce independent formatting context for subgrid.
As part of crbug.com/355215704 we've weakened for containment
requirements for container queries.
We should however still enforce an independent formatting context for
subgrid, as grid will pierce into subgrids, and can't support changing
their style.
Fixed: 369331413
Change-Id: I875f4095116f18f923a0c50c4bf1887c05cea4a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5890347
Commit-Queue: Ian Kilpatrick ikilpatrick@chromium.org
Reviewed-by: Morten Stenshorne mstensho@chromium.org
Cr-Commit-Position: refs/heads/main@{#1359893}