TinyMCE floatpanels sometimes don't adjust position/hide when scrolling

[iseulde]

This is a follow up for #29516.

We now hide panels on scroll unless it's hovered, but in that case it still looks weird and it should be fixed somehow. See #29516 for possible fixes.

The problem here is large dropdowns. They need to be scrollable.

[azaozz]

Thinking that the current behavior is best: hide the drop-down on scroll unless the cursor is over it. Some longer drop-downs have scrollbars, we can't hide them on scrolling. Also lets the users scroll the page when a drop-down is longer than the viewport (the top or bottom is not visible).