Inside the Images Wall snippet, images are dispatched to columns
depending on the height already reached by each column. This computation
relies on a sub-pixel height which leads to a confusing behavior.

This commit rounds the sub-pixel height to a visible pixel height to
avoid the confusion.

Steps to reproduce:
In the default images of the Images Wall snippet, the third image (sign)
is one pixel taller than the other ones.
- Drop an Images Wall snippet.
- Select the "sign" image.
- Move it to the first position.
(Because of another bug involving a race condition with the loading of
images, you might observe a different behavior. Move to first position
again to recompute the layout several times.)

=> The compass image moved to the first column.

task-2990053

X-original-commit: 1fc45be924e904dc595af61e0845b91cc5d24a49
Part-of: odoo/odoo#124608