Before this commit, when trying to delete one
unicode character (e.g. 😍), only one javascript character was delete
but one unicode character (e.g. 😍) could be two javascript characters
as the javascript string is coded in utf-16.
This commit fixes that by calculating the size of one unicode character
from the javascript string.
Task-2658890
closesodoo/odoo#79071
X-original-commit: fea5b87615077f5f41dec8c4d1480f157bbd26ae
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>