GdkWin32: switch to new clipboard API
This is a backport of !1143 (merged) to gtk4.
SetClipboardViewer()
API is obsolete is prone to clipboard chain breaks
from other applications.
Use recommended AddClipboardFormatListener()
instead.
See the reference doc.
Fixes #442 (closed)
Special thanks to @lb90 for the support on discourse for debugging the issue and pinpointing the old gtk+3 fix.
Edited by gwillems