Adds an outline to the popover arrows with anti-aliasing.
//In the screenshots, more contrasting colors are used to make it more visible.//
{F8315542, size=full}
At different UI scales and UI line width:
{F8315543}
This popover arrows has lines at exactly 45 degrees, in that case anti-aliasing (see ref. below) is quite easy to achieve,
by creating a one-pixel edge with low opacity, simply copying and shifting triangles by one pixel.
{F8315545, size=full}
{F8402024, size=full}
The references from the 2D editor:
{F8315544}