Remove generic type of default value in ValueBoundProperty

Currently the default value type in ValueBoundProperty is bound with the presentation type of the field (generic <T>), but it is typically something else (i.e. the model type).

E.g. presentation value of the JCR selects is the Node but the default value is specified as a string.

Symptoms

The problem is most prominent when there is a converter between the model and the presentation types is preset. E.g. this:

field: 
     $type: textField
     type: java.lang.Long
     converterClass: com.vaadin.data.converter.StringToLongConverter
     defaultValue: !!java.lang.Long 0

In the snippet above will cause a CCE for the following reasons:

• SnakeYAML will read the number as hinted by the tag
• Map2Bean will resolve the generic default value type (via getter/setter signature and BeanIntrospection)
• M2B will consequently convert a number to a string and will feed it to the converter chain upon field initialisation, converter will fail.

Solution:

• Be explicit about the type of the default value (by implementing MGNLUI-6374)?
• Be more flexible when setting the default value? I.e. in FormPresenter - do not assume that the value is in "model" form, check if the value is already compatible with presentation form. Consider adding presetation type as [pre-configured] definition property? Do we have a use-case for model type property as well?