[gtk4] Cursor fade in/out
gtk4 text entry boxes don't blink their cursor as on - off, but they fade in - fade out.
With our new blazingly fast rendering, we could also do the same. For a consistent experience, probably only in the gtk4 version.
I-beam and underline cursors should be easier. Block cursor is a bit trickier. It swaps the fg and bg colors (by default), so I guess we'd need to gradually cross-fade the two colors.
We should look at what GTK does exactly (e.g. linear zig-zag, or sine wave etc.) and copy that.
Maybe subject to a setting, API, whatnot.
Consider doing the same for blinking text, too.
Edited by Egmont Koblinger