Merge bitcoin-core/gui#271: Don't clear console prompt when font resizing

7962e0d qt: Do not clear console prompt when font resizing (Hennadii Stepanov)
d2cc339 qt, refactor: Drop redundant history cleaning in RPC console (Hennadii Stepanov)
4f0ae47 qt: Untie irrelevant signal-slot parameters (Hennadii Stepanov)

Pull request description:

  On master, a console resize event will clear the prompt. To fix this, we store the content of the prompt and re-set it upon a resize. This preserves the prompt text throughout resizes. The text will still clear when you click the clear button, as it should.

  **Master**

  | Before Resize      | After Resize |
  | ----------------- | ------------ |
  |  ![master-beforeresize](https://user-images.githubusercontent.com/23396902/113553721-2a428d80-95c6-11eb-971b-bb77151bc6d5.png)  |  ![master-afterresize](https://user-images.githubusercontent.com/23396902/113553769-3d555d80-95c6-11eb-9cdb-9ad1fd7208a9.png) |

  **PR**
  | Before Resize      | After Resize |
  | ----------------- | ------------ |
  | ![pr-beforeresize](https://user-images.githubusercontent.com/23396902/113553885-6f66bf80-95c6-11eb-8317-0975f1ebd444.png) | ![pr-afterresize](https://user-images.githubusercontent.com/23396902/113553906-75f53700-95c6-11eb-9a32-b64d8aba98e5.png) |

  Closes dashpay#269

ACKs for top commit:
  laanwj:
    Code review ACK 7962e0d
  hebasto:
    ACK 7962e0d
  Talkless:
    tACK 7962e0d, tested on Debian Sid with Qt 5.15.2

Tree-SHA512: a6f19d3f80e2e47725cff5d6e15862b6cb793a65dfcaded15f23bba051088cd3317f068f93290c9b09d0a90f5fcac1c5a4610cc417cc5961ba6d005fe5049ab0

Author: laanwj

src/qt/rpcconsole.cpp

@@ -489,7 +489,7 @@ 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, &RPCConsole::clear);
+    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->btnClearTrafficGraph, &QPushButton::clicked, ui->trafficGraph, &TrafficGraphWidget::clear);
@@ -822,7 +822,7 @@ void RPCConsole::setFontSize(int newSize)
 
     // clear console (reset icon sizes, default stylesheet) and re-add the content
     float oldPosFactor = 1.0 / ui->messagesWidget->verticalScrollBar()->maximum() * ui->messagesWidget->verticalScrollBar()->value();
-    clear(false);
+    clear(/* keep_prompt */ true);
     ui->messagesWidget->setHtml(str);
     ui->messagesWidget->verticalScrollBar()->setValue(oldPosFactor * ui->messagesWidget->verticalScrollBar()->maximum());
 }
@@ -873,15 +873,10 @@ void RPCConsole::buildParameterlist(QString arg)
     Q_EMIT handleRestart(args);
 }
 
-void RPCConsole::clear(bool clearHistory)
+void RPCConsole::clear(bool keep_prompt)
 {
     ui->messagesWidget->clear();
-    if(clearHistory)
-    {
-        history.clear();
-        historyPtr = 0;
-    }
-    ui->lineEdit->clear();
+    if (!keep_prompt) ui->lineEdit->clear();
     ui->lineEdit->setFocus();
 
     // Set default style sheet

src/qt/rpcconsole.h

@@ -103,7 +103,7 @@ private Q_SLOTS:
     void updateDetailWidget();
 
 public Q_SLOTS:
-    void clear(bool clearHistory = true);
+    void clear(bool keep_prompt = false);
     void fontBigger();
     void fontSmaller();
     void setFontSize(int newSize);