[Masonry] Implement justify-content/self.

Align items along the grid-axis based on the value for justify-items. We
only account for three values: start, center, and end. This is specified
in the draft spec here:
https://drafts.csswg.org/css-align-3/#content-distribution.

Bug: 343257585
Change-Id: Ib9839734c3daa0664c02a8cf4db65b6a6830c9a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6443323
Reviewed-by: Ethan Jimenez <ethavar@microsoft.com>
Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Reviewed-by: Alison Maher <almaher@microsoft.com>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Ethan Jimenez <ethavar@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1448076}