TextEditor: Sort indent ranges before applying

It can easily happen that callers insert indent ranges out of order, and
without sorting the indentation done earlier in the file is not
considered for the later parts, leading to inconsistent results.

Fixes: QTCREATORBUG-18929
Change-Id: Ice2abe92d54446bcdd102c6a1f822262a8533543
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/utils/changeset.h

@@ -121,4 +121,9 @@ private:
     bool m_error;
 };
 
+inline bool operator<(const ChangeSet::Range &r1, const ChangeSet::Range &r2)
+{
+    return r1.start < r2.start;
+}
+
 } // namespace Utils