Don't serialize grid shorthand if it can't be roundtripped

If we have auto-flow and both grid-template-rows and
grid-template-columns set to non-initial values, the shorthand
can't be serialized, so just return empty string to indicate as
such. This had some coverage in WPT, but adding an additional
case, as well as making the cssText comparison more generic since
property ordering is not specified.

Change-Id: I4176c350dd114b731274f0839454f3f31d0f005b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3853341


Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Ana Sollano Kim <ansollan@microsoft.com>
Auto-Submit: Daniel Libby <dlibby@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1039145}