QSpinbox and QML Spinbox does not support prefixes

Greetings,

Since Qt does not support localised percentage formatting yet, as a KDE translator we use manual percentage positioning on the variable placeholders. This involves placing the percentage sign before the value for Turkish.

However, in QSpinbox and QML spin box, there is no possibility to use a prefix option or a value with modifiable placeholders, only suffix, thus rendering the Turkish translators inoperable for these kind of percentage values, and looks very unprofessional on the interface.

We need prefix support or automatic percentage formatting[1] implemented in order to correctly render Turkish text/values.

 [1] https://bugreports.qt.io/browse/QTBUG-111516