Merge bitcoin#17257: gui: disable font antialiasing for QR image address

e156b9d gui: disable font antialiasing for QR image address (fanquake)

Pull request description:

  The address text inside the QR code is currently fairly blurry / unreadable. Explicitly disabling font antialiasing improves that somewhat.

  master (693e400):
  ![macOS_master](https://user-images.githubusercontent.com/863730/67591414-644e0580-f72b-11e9-8399-2cd0584e7d62.png)

  PR (e156b9d):
  ![macOS_pr](https://user-images.githubusercontent.com/863730/67591424-6dd76d80-f72b-11e9-86b6-b3911f8e07e6.png)

ACKs for top commit:
  laanwj:
    ACK e156b9d

Tree-SHA512: 32aeb2ffe8164a1006f80e76c6e413fcb88e32ced42d2b2af69cca908bd32673f3e379184be917f1870864b940db943e7f46a7ecb0779343d5d129b381660c38

Author: laanwj

src/qt/qrimagewidget.cpp

@@ -71,6 +71,7 @@ bool QRImageWidget::setQR(const QString& data, const QString& text)
 
     if (!text.isEmpty()) {
         QFont font = GUIUtil::fixedPitchFont();
+        font.setStyleStrategy(QFont::NoAntialias);
         QRect paddedRect = qrAddrImage.rect();
 
         // calculate ideal font size