widgets: Add MacOS-compatible menu separator
This patch attempts to fix one of the items in issue 9877.
The separator in the search menu uses a character that does not render on MacOS. I added an #ifdef
to show a valid character on MacOS for the next release. In the future, we might consolidate to a single character that renders on all platforms.
@lukaso, hi! Let me know if this fixes the issue. It'd be nice to have the search box look a little better for the 2.99.18 release on MacOS.