HighlightInheritance: fix ‘text-shadow’ with font-relative units

The values of properties not applicable to highlight pseudos generally
don’t matter, but font properties can affect ‘text-shadow’ if offsets
use font- or glyph-relative units.

This patch copies those properties from the originating style when
initialising highlight styles, as resolved in csswg-drafts#7591 [1].

[1] https://github.com/w3c/csswg-drafts/issues/7591

Fixed: 1350476
Change-Id: I222d9d58f44adaba39a68180e87efae2fd57d1d8
Cq-Do-Not-Cancel-Tryjobs: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3818830
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1062958}