[Gap Decorations]: Implement grid gap decorations for fragmentation

This CL begins the implementation of grid gap decorations for
fragmentation. To support fragmentation, row gaps that are either split
or are the last content in a fragmentainer HAVE to be suppressed [1].
This change addresses this by: (1) Modifying intrinsic block size item
offsets based on the delta of any gap that extends beyond the
fragmentainer (2) Excluding such gaps from the fragment relative gap
geometry.

The implementation details in this change involves recording the
original gap positions in a non-fragmented context, then "PlaceGaps"
uses this geometry during fragmentation. If a gap doesn't fit in the
current fragmentainer, the last placed gap is considered as a
suppression candidate. It is suppressed if it's the last content in the
fragmentainer or is split across multiple fragmentainers.

Test cases as wpts have been added to exercise this change. Future
changes will address spanning items and `rule-break` functionality in
fragmented grids, subgrid, and eventually add fragmentation support for
gap decorations in flex and multi-column layouts.

[1]: https://github.com/w3c/csswg-drafts/issues/11520

Bug: 357648037, 394042462
Change-Id: I4dd123cf9a59b4d70eedee61ae99ab2fe8de011a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6900436
Reviewed-by: Alison Maher <almaher@microsoft.com>
Commit-Queue: Sam Davis Omekara <samomekarajr@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1519628}