Merge bitcoin-core/gui#329: Make console buttons look clickable

8b419b5 qt: make console buttons look clickable (Jarol Rodriguez)

Pull request description:

  On master, for macOS, the console buttons' hitboxes are quite small. This makes clicking on the button with your mouse a little more tedious than it should be. The Issue is related to recent versions of Qt (>5.9.8) not playing so nice on macOS when there are "incorrect" `width` and `height` values set for a `QPushButton` (here is another example: bitcoin-core/gui#319 (review)).

  This fixes this small hitbox issue by converting the buttons from `QPushButton` to `QToolButton`, which in turn makes the buttons look explicitly clickable. This approach was chosen as it helps us avoid having to play around with `width` and `height` values until we find values that play nice with macOS and look good on Linux & Windows. Also, `QToolButton` is an appropriate class for these buttons.

  Per [Qt Docs](https://doc.qt.io/qt-5/qtoolbutton.html#details):
  > A tool button is a special button that provides quick-access to specific commands or options. As opposed to a normal command button, a tool button usually doesn't show a text label, but shows an icon instead.

  Since we are changing the type of the buttons, we need to change the respective actions connection logic in `rpcconsole`. Instead of plugging in `QToolButton`, we abstract it to the base class: `QAbstractButton`.

  per [Qt Dev Notes](https://github.com/bitcoin-core/bitcoin-devwiki/wiki/Developer-Notes-for-Qt-Code#inherited-signals-and-slot)
  > Use base class functions as this makes the code more general, e.g., use QAbstractButton::clicked instead of QPushButton::clicked.

  While here, we also update the size of the icons to `22x22` to be consistent with other tool buttons.

  **macOS: Master vs PR:**

  | Master        | PR               |
  | ----------- | ----------- |
  | ![master-ss-macos](https://user-images.githubusercontent.com/23396902/118339460-e9079c80-b4e6-11eb-864b-d394aca5df61.png) | ![pr-ss-macos](https://user-images.githubusercontent.com/23396902/118339468-ec9b2380-b4e6-11eb-9a9e-30620216750e.png) |

  **Linux: Master vs PR:**

  | Master        | PR               |
  | ----------- | ----------- |
  | ![master-ss-linux](https://user-images.githubusercontent.com/23396902/118339520-13595a00-b4e7-11eb-86d0-96dd1264c198.png) | ![pr-ss-linux](https://user-images.githubusercontent.com/23396902/118339533-1c4a2b80-b4e7-11eb-8d7f-f733d999c8fd.png) |

ACKs for top commit:
  hebasto:
    ACK 8b419b5, tested on Linux Mint 20.1 (Qt 5.12.8).
  promag:
    Tested ACK 8b419b5 on macOS Big Sur M1, this drops only relevant usages to `flat` buttons.

Tree-SHA512: 3f3cdcbe83398136a1d1ee8fc2835be8681f2ed39e79db1e939cab6a00a779f528343d54992807a845cc84d9ef13591affb7a6dbca9e5753a2b8665b0af4d611

src/qt/rpcconsole.cpp

@@ -37,6 +37,7 @@
 #include <wallet/walletutil.h>
 #endif
 
+#include <QAbstractButton>
 #include <QButtonGroup>
 #include <QDir>
 #include <QFont>
@@ -547,9 +548,9 @@ RPCConsole::RPCConsole(interfaces::Node& node, QWidget* parent, Qt::WindowFlags
     ui->lineEdit->setMaxLength(16 * 1024 * 1024);
     ui->messagesWidget->installEventFilter(this);
 
-    connect(ui->clearButton, &QPushButton::clicked, [this] { clear(); });
-    connect(ui->fontBiggerButton, &QPushButton::clicked, this, &RPCConsole::fontBigger);
-    connect(ui->fontSmallerButton, &QPushButton::clicked, this, &RPCConsole::fontSmaller);
+    connect(ui->clearButton, &QAbstractButton::clicked, [this] { clear(); });
+    connect(ui->fontBiggerButton, &QAbstractButton::clicked, this, &RPCConsole::fontBigger);
+    connect(ui->fontSmallerButton, &QAbstractButton::clicked, this, &RPCConsole::fontSmaller);
     connect(ui->btnClearTrafficGraph, &QPushButton::clicked, ui->trafficGraph, &TrafficGraphWidget::clear);
 
     // disable the wallet selector by default