Base: Drop QString-std::string conversion functions from Tools

Convenience helpers function Tools::toStdString and Tools::fromStdString
were implemented for Qt4 or older to perform utf8 aware conversion as
QString::toStdString/QString::fromStdString were using toAscii/fromAscii
internally (see https://dreamswork.github.io/qt4/classQString.html).

Since Qt5 QString uses toUtf8/fromUTf8, which makes the helper functions
obsolete (see https://doc.qt.io/qt-5/qstring.html#fromStdString).

src/Mod/Sketcher/Gui/Utils.cpp

@@ -31,7 +31,6 @@
 
 #include <App/Application.h>
 #include <Base/Quantity.h>
-#include <Base/Tools.h>
 #include <Base/UnitsApi.h>
 #include <Gui/CommandT.h>
 #include <Gui/Document.h>
@@ -723,7 +722,7 @@ std::string SketcherGui::lengthToDisplayFormat(double value, int digits)
     QString qUserString = asQuantity.getUserString();
     if (Base::UnitsApi::isMultiUnitLength() || (!hideUnits() && useSystemDecimals())) {
         // just return the user string
-        return Base::Tools::toStdString(qUserString);
+        return qUserString.toStdString();
     }
 
     // find the unit of measure
@@ -738,24 +737,23 @@ std::string SketcherGui::lengthToDisplayFormat(double value, int digits)
     QRegularExpressionMatch match = rxNoUnits.match(qUserString);
     if (!match.hasMatch()) {
         // no units in userString?
-        return Base::Tools::toStdString(qUserString);
+        return qUserString.toStdString();
     }
     QString matched = match.captured(1);  // matched is the numeric part of user string
     int dpPos = matched.indexOf(QLocale().decimalPoint());
     if (dpPos < 0) {
+        auto ret = matched.toStdString();
         // no decimal separator (ie an integer), return all the digits
-        if (hideUnits()) {
-            return Base::Tools::toStdString(matched);
-        }
-        else {
-            return Base::Tools::toStdString(matched + unitPart);
+        if (!hideUnits()) {
+            ret.append(unitPart.toStdString());
         }
+        return ret;
     }
 
     // real number
     if (useSystemDecimals() && hideUnits()) {
         // return just the numeric part of the user string
-        return Base::Tools::toStdString(matched);
+        return matched.toStdString();
     }
 
     // real number and not using system decimals
@@ -764,11 +762,11 @@ std::string SketcherGui::lengthToDisplayFormat(double value, int digits)
         // just take the whole thing
         requiredLength = matched.size();
     }
-    QString numericPart = matched.left(requiredLength);
-    if (hideUnits()) {
-        return Base::Tools::toStdString(numericPart);
+    auto numericPart = matched.left(requiredLength).toStdString();
+    if (!hideUnits()) {
+        numericPart.append(unitPart.toStdString());
     }
-    return Base::Tools::toStdString(numericPart + unitPart);
+    return numericPart;
 }
 
 // convert value to display format %0.[digits]f. Units are always displayed for
@@ -791,7 +789,7 @@ std::string SketcherGui::angleToDisplayFormat(double value, int digits)
         QString escapeSecond = QString::fromLatin1("\"");          // substitute ascii double quote
         QString displayString = qUserString.replace(schemeMinute, escapeMinute);
         displayString = displayString.replace(schemeSecond, escapeSecond);
-        return Base::Tools::toStdString(displayString);
+        return displayString.toStdString();
     }
 
     // we always use use U+00B0 (°) as the unit of measure for angles in
@@ -805,19 +803,21 @@ std::string SketcherGui::angleToDisplayFormat(double value, int digits)
     QRegularExpressionMatch match = rxNoUnits.match(qUserString);
     if (!match.hasMatch()) {
         // no units in userString?
-        return Base::Tools::toStdString(qUserString);
+        return qUserString.toStdString();
     }
     QString matched = match.captured(1);  // matched is the numeric part of user string
+    auto smatched = matched.toStdString();
+    auto sUnitString = qUnitString.toStdString();
     int dpPos = matched.indexOf(decimalSep);
     if (dpPos < 0) {
         // no decimal separator (ie an integer), return all the digits
-        return Base::Tools::toStdString(matched + qUnitString);
+        return smatched + sUnitString;
     }
 
     // real number
     if (useSystemDecimals()) {
         // return just the numeric part of the user string + degree symbol
-        return Base::Tools::toStdString(matched + qUnitString);
+        return smatched + sUnitString;
     }
 
     // real number and not using system decimals
@@ -826,8 +826,9 @@ std::string SketcherGui::angleToDisplayFormat(double value, int digits)
         // just take the whole thing
         requiredLength = matched.size();
     }
-    QString numericPart = matched.left(requiredLength);
-    return Base::Tools::toStdString(numericPart + qUnitString);
+    auto numericPart = matched.left(requiredLength).toStdString();
+    numericPart.append(sUnitString);
+    return numericPart;
 }