Block modifier-letter-voicing character from domain names

This character (ˬ) is easy to miss between other characters. It's one of the three characters from Spacing-Modifier-Letters block that ICU lists in its recommended set in uspoof.cpp. Two of these characters (modifier-letter-turned-comma and modifier-letter-apostrophe) are already blocked in crbug/678812.

Bug: 896717
Change-Id: I24b2b591de8cc7822cd55aa005b15676be91175e
Reviewed-on: https://chromium-review.googlesource.com/c/1303037
Commit-Queue: Mustafa Emre Acer <meacer@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604128}