[text-box-trim] Test accumulations

This patch adds a test for when the element to trim has
different `text-box-edge` value from the `text-box-edge` value
of the element that has `text-box-trim`. Discussed and
resolved at:
https://github.com/w3c/csswg-drafts/issues/5426

Bug: 40254880
Change-Id: I5685fbaebddb8c7429b3b041c5fe0f88b982fc3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5547563
Auto-Submit: Koji Ishii <kojii@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1303166}