[StyleBuilder] Expose ComputedStyleBuilder::CloneStyle().

And use in place of ComputedStyle::Clone(*state.Style()) calls.
There should be no behaviour change.

Bug: 1377295
Change-Id: I17cef9fd918e099ec28232874ef059bdc3873e4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4028824


Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1072411}