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

2a45134 qt: Add shortcuts for console font resize buttons (Hennadii Stepanov)
a2e122f qt: Add GUIUtil::AddButtonShortcut (Hennadii Stepanov)
4ee9ee7 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 2a45134
  Talkless:
    tACK 2a45134, tested on Debian Sid with Qt 5.15.2, shortcuts still work.

Tree-SHA512: e894ccb7e5c695ba83998c21a474d6c587c9c849f12ced665c5e0034feb6b143e41b32ba135cab6cfab22cbf153d5a52b1083b2a278e6dfca3f5ad14c0f6c573

src/qt/guiutil.cpp

@@ -340,6 +340,11 @@ void setupAppearance(QWidget* parent, OptionsModel* model)
     }
 }
 
+void AddButtonShortcut(QAbstractButton* button, const QKeySequence& shortcut)
+{
+    QObject::connect(new QShortcut(shortcut, button), &QShortcut::activated, [button]() { button->animateClick(); });
+}
+
 bool parseBitcoinURI(const QUrl &uri, SendCoinsRecipient *out)
 {
     // return if URI is not valid or is no dash: URI

src/qt/guiutil.h

@@ -44,6 +44,7 @@ class QAction;
 class QButtonGroup;
 class QDateTime;
 class QFont;
+class QKeySequence;
 class QLineEdit;
 class QMenu;
 class QPoint;
@@ -135,6 +136,14 @@ namespace GUIUtil
     // Setup appearance settings if not done yet
     void setupAppearance(QWidget* parent, OptionsModel* model);
 
+    /**
+     * 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 "dash:" URI into recipient object, return true on successful parsing
     bool parseBitcoinURI(const QUrl &uri, SendCoinsRecipient *out);
     bool parseBitcoinURI(QString uri, SendCoinsRecipient *out);

src/qt/rpcconsole.cpp

@@ -936,20 +936,23 @@ void RPCConsole::clear(bool keep_prompt)
             ).arg(consoleFontSize)
         );
 
-#ifdef Q_OS_MAC
-    QString clsKey = "(⌘)-L";
-#else
-    QString clsKey = "Ctrl-L";
-#endif
-
-    message(CMD_REPLY, (tr("Welcome to the %1 RPC console.").arg(PACKAGE_NAME) + "<br>" +
-                        tr("Use up and down arrows to navigate history, and %1 to clear screen.").arg("<b>"+clsKey+"</b>") + "<br>" +
-                        tr("Type %1 for an overview of available commands.").arg("<b>help</b>") + "<br>" +
-                        tr("For more information on using this console type %1.").arg("<b>help-console</b>") +
-                        "<br><span class=\"secwarning\"><br>" +
-                        tr("WARNING: Scammers have been active, telling users to type commands here, stealing their wallet contents. Do not use this console without fully understanding the ramifications of a command.") +
-                        "</span>"),
-                        true);
+    message(CMD_REPLY,
+            tr("Welcome to the %1 RPC console.").arg(PACKAGE_NAME) +
+                "<br>" +
+                tr("Use up and down arrows to navigate history, and %1 to clear screen.")
+                    .arg("<b>" + ui->clearButton->shortcut().toString(QKeySequence::NativeText) + "</b>") +
+                "<br>" +
+                tr("Use %1 and %2 to increase or decrease the font size.")
+                    .arg("<b>" + ui->fontBiggerButton->shortcut().toString(QKeySequence::NativeText) + "</b>")
+                    .arg("<b>" + ui->fontSmallerButton->shortcut().toString(QKeySequence::NativeText) + "</b>") +
+                "<br>" +
+                tr("Type %1 for an overview of available commands.").arg("<b>help</b>") +
+                "<br>" +
+                tr("For more information on using this console type %1.").arg("<b>help-console</b>") +
+                "<br><span class=\"secwarning\"><br>" +
+                tr("WARNING: Scammers have been active, telling users to type commands here, stealing their wallet contents. Do not use this console without fully understanding the ramifications of a command.") +
+                "</span>",
+            true);
 }
 
 void RPCConsole::keyPressEvent(QKeyEvent *event)
@@ -1285,8 +1288,18 @@ void RPCConsole::setButtonIcons()
 {
     const QSize consoleButtonsSize(BUTTON_ICONSIZE * 0.8, BUTTON_ICONSIZE * 0.8);
     GUIUtil::setIcon(ui->clearButton, "remove", GUIUtil::ThemedColor::RED, consoleButtonsSize);
+
     GUIUtil::setIcon(ui->fontBiggerButton, "fontbigger", GUIUtil::ThemedColor::BLUE, consoleButtonsSize);
+    //: Main shortcut to increase the RPC console font size.
+    ui->fontBiggerButton->setShortcut(tr("Ctrl++"));
+    //: Secondary shortcut to increase the RPC console font size.
+    GUIUtil::AddButtonShortcut(ui->fontBiggerButton, tr("Ctrl+="));
+
     GUIUtil::setIcon(ui->fontSmallerButton, "fontsmaller", GUIUtil::ThemedColor::BLUE, consoleButtonsSize);
+    //: Main shortcut to decrease the RPC console font size.
+    ui->fontSmallerButton->setShortcut(tr("Ctrl+-"));
+    //: Secondary shortcut to decrease the RPC console font size.
+    GUIUtil::AddButtonShortcut(ui->fontSmallerButton, tr("Ctrl+_"));
 }
 
 void RPCConsole::reloadThemedWidgets()