Merge bitcoin-core/gui#281: set shortcuts for console's resize buttons

2a45134b5694c12546d77cdff541612881f7e3e7 qt: Add shortcuts for console font resize buttons (Hennadii Stepanov)
a2e122f0fe72d695762db2b83905e246f451300c qt: Add GUIUtil::AddButtonShortcut (Hennadii Stepanov)
4ee9ee72363d46c5ba0c71b8d8283d9c5621e3ed qt: Use native presentation of shortcut (Hennadii Stepanov)

Pull request description:

  On `master` the only way to resize the console font is to manually move your mouse and click the resize buttons. This PR introduces convenient keyboard shortcuts to resize the console font.

  The common resize shortcuts for applications are `Ctrl+=`/`Ctrl++` and `Ctrl+-`/`Ctrl+_`. This means that the resize QPushButtons need two shortcuts each, but you cannot assign multiple shortcuts to a QPushButton. See: https://doc.qt.io/qt-5/qabstractbutton.html#shortcut-prop

  To get around this, we introduce a new function in `guiutil`, which connects a supplied `QKeySequence` shortcut to a `QAbstractButton`. This function can be reused in other situations where more than one shortcut is needed for a button.

  | PR on macOS      | PR on Linux |
  | ---------------- | ------------ |
  |  ![mac-resize-shortcuts](https://user-images.githubusercontent.com/23396902/114750132-a2752580-9d21-11eb-9542-15716f2c257d.gif) | ![linux-resize-shortcuts](https://user-images.githubusercontent.com/23396902/114750165-aacd6080-9d21-11eb-8abc-5388690dcf0b.gif) |

ACKs for top commit:
  hebasto:
    re-ACK 2a45134b5694c12546d77cdff541612881f7e3e7
  Talkless:
    tACK 2a45134b5694c12546d77cdff541612881f7e3e7, tested on Debian Sid with Qt 5.15.2, shortcuts still work.

Tree-SHA512: e894ccb7e5c695ba83998c21a474d6c587c9c849f12ced665c5e0034feb6b143e41b32ba135cab6cfab22cbf153d5a52b1083b2a278e6dfca3f5ad14c0f6c573

1 files changed, 10 insertions, 0 deletions

diff --git a/src/qt/guiutil.h b/src/qt/guiutil.h
index a1cf274354..9c2ad74e1e 100644
--- a/src/qt/guiutil.h
+++ b/src/qt/guiutil.h
@@ -36,10 +36,12 @@ namespace interfaces
 }
 
 QT_BEGIN_NAMESPACE
+class QAbstractButton;
 class QAbstractItemView;
 class QAction;
 class QDateTime;
 class QFont;
+class QKeySequence;
 class QLineEdit;
 class QMenu;
 class QPoint;
@@ -65,6 +67,14 @@ namespace GUIUtil
     // Set up widget for address
     void setupAddressWidget(QValidatedLineEdit *widget, QWidget *parent);
 
+    /**
+     * Connects an additional shortcut to a QAbstractButton. Works around the
+     * one shortcut limitation of the button's shortcut property.
+     * @param[in] button    QAbstractButton to assign shortcut to
+     * @param[in] shortcut  QKeySequence to use as shortcut
+     */
+    void AddButtonShortcut(QAbstractButton* button, const QKeySequence& shortcut);
+
     // Parse "bitcoin:" URI into recipient object, return true on successful parsing
     bool parseBitcoinURI(const QUrl &uri, SendCoinsRecipient *out);
     bool parseBitcoinURI(QString uri, SendCoinsRecipient *out);