hterm: size notification: use × instead of x
hterm: size notification: use × instead of x

We can handle Unicode just fine, so use × to display the dimensions.
This feels more proper than an ASCII x, and aligns with at least what
Wikipedia says:
https://en.wikipedia.org/wiki/Multiplication_sign#Uses
> Geometric dimension of an object, such as noting that a room is
> 10 feet × 12 feet in area.

Change-Id: Ia4a47fbcd94efb6a1b8ee0c9a5ff4a853659dd92
Reviewed-on: https://chromium-review.googlesource.com/c/apps/libapps/+/2563929
Reviewed-by: Joel Hockey <9ecfc52dc2ffef73afac73f3495f294aeddf1231@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm