[wpt] upgrade contenteditable tests to non-tentative
These are supported cross vendor:
https://wpt.fyi/results/contenteditable?label=experimental&label=master&aligned&q=tentative
Bug: 3534256
Change-Id: Iecfdf4530330f1f265be52d99bebadfea6eed70e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5713771
Commit-Queue: Ari Chivukula arichiv@chromium.org
Auto-Submit: Ari Chivukula arichiv@chromium.org
Reviewed-by: Steven Bingler bingler@chromium.org
Commit-Queue: Steven Bingler bingler@chromium.org
Cr-Commit-Position: refs/heads/main@{#1328197}