Partially revert "Remove unused stringutils methods"

This partially reverts commit 0c1a5a5c97.

src/blackmisc/simulation/xplane/aircraftmodelloaderxplane.cpp

@@ -569,7 +569,7 @@ namespace BlackMisc::Simulation::XPlane
         {
             ++lineNum;
             QString line = in.readLine();
-            auto tokens = line.split(' ');
+            auto tokens = splitString(line, [](QChar c) { return c.isSpace(); });
             if (!tokens.empty())
             {
                 auto it = commands.find(tokens[0]);
@@ -615,7 +615,7 @@ namespace BlackMisc::Simulation::XPlane
             ++lineNum;
             QString line = in.readLine();
             if (line.isEmpty() || line[0] == '#') continue;
-            auto tokens = line.split(' ');
+            auto tokens = splitString(line, [](QChar c) { return c.isSpace(); });
             if (!tokens.empty())
             {
                 auto it = commands.find(tokens[0]);

src/blackmisc/stringutils.cpp

@@ -29,6 +29,11 @@ namespace BlackMisc
         return splitStringRefs(s, [](QChar c) { return c == '\n' || c == '\r'; });
     }
 
+    QStringList splitLines(const QString &s)
+    {
+        return splitString(s, [](QChar c) { return c == '\n' || c == '\r'; });
+    }
+
     QByteArray utfToPercentEncoding(const QString& s, const QByteArray &allow, char percent)
     {
         QByteArray result;

src/blackmisc/stringutils.h

@@ -12,6 +12,7 @@
 #define BLACKMISC_STRINGUTILS_H
 
 #include "blackmisc/blackmiscexport.h"
+#include "blackmisc/range.h"
 #include "blackmisc/typetraits.h"
 
 #include <QByteArray>
@@ -116,6 +117,15 @@ namespace BlackMisc
     //! It would be risky to call splitLinesRefs with an rvalue, so forbid it.
     void splitLinesRefs(const QString &&) = delete;
 
+    //! Split a string into multiple strings, using a predicate function to identify the split points.
+    template <class F> QStringList splitString(const QString &s, F predicate)
+    {
+        return makeRange(splitStringRefs(s, predicate)).transform([](QStringRef sr) { return sr.toString(); });
+    }
+
+    //! Split a string into multiple lines. Blank lines are skipped.
+    BLACKMISC_EXPORT QStringList splitLines(const QString &s);
+
     //! Extended percent encoding supporting UTF-16
     BLACKMISC_EXPORT QByteArray utfToPercentEncoding(const QString &s, const QByteArray &allow = {}, char percent = '%');