form.field.Number: verify if manual inputs honor stepSizes < 1

i changed the number evaluation from onInputValueChange() to onFocusLeave().

e.g. in case you want to type 0.01, typing 0.0 would adjust the field value to 0 in real time, so it would be impossible to enter it manually (without using spin buttons or arrow keys).

so, it needs to be possible to enter "invalid" values and the field evaluation needs to happen when the field loses focus.