qt: Do not use QClipboard::Selection on Windows and macOS.
qt: Do not use QClipboard::Selection on Windows and macOS.

Windows and macOS do not support the global mouse selection.

Github-Pull: bitcoin-core/gui#277
Rebased-From: 7f3a5980c1d54988a707b961fd2ef647cebb4c5b

rnicoll/dogecoin,rnicoll/dogecoin,rnicoll/dogecoin,rnicoll/dogecoin,rnicoll/dogecoin