Merge #14725: qt: Bump the minimum Qt version to 5.2

2bc3f114d09a9798d166896b0145b69c5ed2d41e Bump the minimum Qt version to 5.2 (Hennadii Stepanov)

Pull request description:

  Refs:
  - #13478
  - https://github.com/bitcoin/bitcoin/issues/13478#issuecomment-438431556 by @MarcoFalke

Tree-SHA512: b598a80f25df9c440e0776b373b88a305250582049ab60caee48375f6599c2f6d40ed94b488ff3604ec9fc12c71f440f6881a3fc656c81f99e89dc5bf9ea2f6d
(cherry picked from commit 74213fa4d13e53c3811d69a516fc865b79fdd0c7)

# Conflicts:
#	build-aux/m4/bitcoin_qt.m4
#	src/qt/dash.cpp
#	src/qt/guiutil.cpp
#	src/qt/splashscreen.cpp

build-aux/m4/bitcoin_qt.m4

@@ -291,7 +291,7 @@ AC_DEFUN([_BITCOIN_QT_CHECK_QT5],[
       #endif
     ]],
     [[
-      #if QT_VERSION < 0x050000
+      #if QT_VERSION < 0x050200 || QT_VERSION_MAJOR < 5
       choke
       #endif
     ]])],

src/qt/dash.cpp

@@ -566,14 +566,12 @@ int main(int argc, char *argv[])
 
     // Do not refer to data directory yet, this can be overridden by Intro::pickDataDirectory
 
-    /// 1. Basic Qt initialization (not dependent on parameters or configuration)
+    /// 2. Basic Qt initialization (not dependent on parameters or configuration)
     Q_INIT_RESOURCE(dash);
     Q_INIT_RESOURCE(dash_locale);
 
-#if QT_VERSION > 0x050100
     // Generate high-dpi pixmaps
     QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
-#endif
 #if QT_VERSION >= 0x050600
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
 #endif

src/qt/guiutil.cpp

@@ -47,6 +47,8 @@
 #include <QDoubleValidator>
 #include <QFileDialog>
 #include <QFont>
+#include <QFontDatabase>
+#include <QKeyEvent>
 #include <QLineEdit>
 #include <QSettings>
 #include <QTextDocument> // for Qt::mightBeRichText
@@ -54,11 +56,6 @@
 #include <QUrlQuery>
 #include <QMouseEvent>
 
-
-#if QT_VERSION >= 0x50200
-#include <QFontDatabase>
-#endif
-
 static fs::detail::utf8_codecvt_facet utf8;
 
 #if defined(Q_OS_MAC)
@@ -150,13 +147,7 @@ QString dateTimeStr(qint64 nTime)
 
 QFont fixedPitchFont()
 {
-#if QT_VERSION >= 0x50200
     return QFontDatabase::systemFont(QFontDatabase::FixedFont);
-#else
-    QFont font("Monospace");
-    font.setStyleHint(QFont::Monospace);
-    return font;
-#endif
 }
 
 // Just some dummy data to generate an convincing random-looking (but consistent) address