Update ios wptrunner config with Xcode and shard.

1. Pass the xcode version to run wpt tests.
2. Increase shard and timeout to be the same as android.

Bug: 1351820
Change-Id: I75938908f1ba78458deabc9373f37b8ccaaccb97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4338280


Commit-Queue: Jie Sheng <jiesheng@google.com>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118225}