[FIX] web: fix scroll to affixed header not fluid

This commit improves the smoothness of the scroll animation to an
affixed header.

As in this case, we stop and continue the animation several times in the
"scrollTo" function, we need to force the easing of the animation to
"linear" when the scroll animation is restarted in the "progress" of
"animate".

task-2773973

X-original-commit: 1770f61ebd9ebd0991ee13a93f0e771c9c0ad698
Part-of: odoo/odoo#96067

addons/web/static/src/legacy/js/core/dom.js

@@ -600,6 +600,7 @@ var dom = {
                 $scrollable.stop();
                 dom.scrollTo(el, Object.assign({}, options, {
                     duration: remainingMs,
+                    easing: 'linear',
                 })).then(() => resolve());
             };