The sequence show -> raise -> activateWindow is factored out to the new function GUIUtil::bringToFront where a macOS fix is added in order to fix #13829.
Partial backport of core PR14123 (commit 5796671)
https://github.com/bitcoin/bitcoin/pull/14123/commits/5796671e1dd8a2d0b1e750c2dce19a10af624095
Depends on D4481.