QtCore: use new QChar::fromUcs{2,4}()

Also replace one case of QChar(0) with QChar::Null.

These were errors in my local tree, which means they're included in
bootstrap builds (incl. qmake).

Change-Id: I3dffa9383fd1a30aa43fe2491ad95bb2b1869b40
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/codecs/qutfcodec.cpp

@@ -821,7 +821,7 @@ QString QUtf16::convertToUnicode(const char *chars, int len, QTextCodec::Convert
                             endian = BigEndianness;
                         } else {
                             endian = LittleEndianness;
-                            ch = QChar((ch.unicode() >> 8) | ((ch.unicode() & 0xff) << 8));
+                            ch = QChar::fromUcs2((ch.unicode() >> 8) | ((ch.unicode() & 0xff) << 8));
                         }
                         *qch++ = ch;
                     }
@@ -951,12 +951,8 @@ QString QUtf32::convertToUnicode(const char *chars, int len, QTextCodec::Convert
                 }
             }
             uint code = (endian == BigEndianness) ? qFromBigEndian<quint32>(tuple) : qFromLittleEndian<quint32>(tuple);
-            if (QChar::requiresSurrogates(code)) {
+            for (char16_t c : QChar::fromUcs4(code))
-                *qch++ = QChar(QChar::highSurrogate(code));
+                *qch++ = c;
-                *qch++ = QChar(QChar::lowSurrogate(code));
-            } else {
-                *qch++ = QChar(code);
-            }
             num = 0;
         }
     }

src/corelib/kernel/qvariant.cpp

@@ -525,14 +525,14 @@ static bool convert(const QVariant::Private *d, int t, void *result, bool *ok)
         case QMetaType::Short:
         case QMetaType::Long:
         case QMetaType::Float:
-            *c = QChar(ushort(qMetaTypeNumber(d)));
+            *c = QChar::fromUcs2(qMetaTypeNumber(d));
             break;
         case QMetaType::UInt:
         case QMetaType::ULongLong:
         case QMetaType::UChar:
         case QMetaType::UShort:
         case QMetaType::ULong:
-            *c = QChar(ushort(qMetaTypeUNumber(d)));
+            *c = QChar::fromUcs2(qMetaTypeUNumber(d));
             break;
         default:
             return false;

src/corelib/serialization/qjsonparser.cpp

@@ -922,12 +922,7 @@ bool Parser::parseString()
                 return false;
             }
         }
-        if (QChar::requiresSurrogates(ch)) {
+        ucs4.append(QChar::fromUcs4(ch));
-            ucs4.append(QChar::highSurrogate(ch));
-            ucs4.append(QChar::lowSurrogate(ch));
-        } else {
-            ucs4.append(QChar(ushort(ch)));
-        }
     }
     ++json;
 

src/corelib/text/qlocale.cpp

@@ -3897,7 +3897,7 @@ bool QLocaleData::numberToCLocale(QStringView s, QLocale::NumberOptions number_o
 
         char out = numericToCLocale(in);
         if (out == 0) {
-            const QChar simple(in.size() == 1 ? in.front() : QChar(0));
+            const QChar simple = in.size() == 1 ? in.front() : QChar::Null;
             if (in == listSeparator())
                 out = ';';
             else if (in == percentSign())