Make QDir::cleanPath documentation less misleading

The code doesn't convert anything that might be a separator on other
platforms (most notably, '\') to '/', it only replaces platform-native
separators (i.e. '\' if running on Windows) with '/'.

Change-Id: I2e241b88b8bd271dfa5d7db61402fe8ef9a6bb6f
Fixes: QTBUG-79736
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/io/qdir.cpp

@@ -2372,8 +2372,9 @@ static QString qt_cleanPath(const QString &path, bool *ok)
 }
 
 /*!
-    Returns \a path with directory separators normalized (converted to "/") and
-    redundant ones removed, and "."s and ".."s resolved (as far as possible).
+    Returns \a path with directory separators normalized (that is, platform-native
+    separators converted to "/") and redundant ones removed, and "."s and ".."s
+    resolved (as far as possible).
 
     Symbolic links are kept. This function does not return the
     canonical path, but rather the simplest version of the input.