Plumbing for resolving % padding/margin against block-size.

Unlike regular CSS boxes, block-start/end percentage-based @page margin
and padding are resolved against the block-size of the containing block,
not against the inline-size.

This CL doesn't fix that, but contains all the plumbing needed.

Also investigated why PercentageResolutionBlockSize() is indefinite in
some cases, and added a comment. It would be neat if this only happened
in measure passes, and then DHCECK for that, however, that would trigger
in a lot of grid layout tests. It would also trigger for flex layout in
some cases, but that merely seems to be a missing call to SetCacheSlot()
in BuildSpaceForFlexBasis().

No behavior changes intended.

Bug: 40286153
Change-Id: I6fed6bd657994ac9542ef74930ade1c232fcf827
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5384259
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278150}