[macOS] Slow perf/repaint when resizing columns in Avalonia 11

[danipen]

Hi, this issue happens only in macOS.

We experience slow performance (or probably that the control is not repainted until you stop dragging) when moving the columns header splitter in the TreeDataGrid.

https://user-images.githubusercontent.com/501613/228465740-a28c0961-425c-432b-9564-e96972c651d3.mov

@grokys @wieslawsoltes @jmacato can you reproduce it too? I'm just trying latest changes on master.

[danipen]

Note that under windows, the resize is normal:

[danipen]

@grokys do you think this PR resoves this issue?

[grokys]

No, that PR is unrelated I'm afraid. I'm no closer to understanding why macOS is slowing down when using an opaque background, unfortunately.