TextInput lacks persistentSelection property that is available for TextEdit

One of the design principles of QtQuick's has been to keep the functionality between similar elements identical and also as style-independent as possible. TextInput selection is always cleared on focus loss, with TextEdit this only happens when persistentSelection property has been set to true. The lack of persistentSelection property creates unnecessary inconsistency between the elements and makes it difficult to customise selection behavior when TextInput comes with implicit functionality that cannot be disabled.

See related issue QTBUG-15341.