[FIX] web_editor: fix black line problem for odd width images

When adding an odd width images on website, a thin black line is
drawn on its right side. The problem comes from the getSourceCanvas
of the cropperjs library. A translation is applied followed by an other
translation in the opposite direction. However the second translation
was not the exact reverse of the first due to a rounding problem.

The fix proposed here comes from: https://github.com/fengyuanchen/cropperjs/pull/300/commits/a6481c052cfc93ef14dd95a3bd00142215dda36e



task-2652904

closes odoo/odoo#77039

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>