Use the Target Element BindingContext instead of the Page VM

[dansiegel]

Description of Change

Fixes bug with the Binding Context of the ParentPageAwareExtension base XAML Extension setting the BindingContext to the Parent Page's Binding Context instead of the Target Element's Binding Context.

Bugs Fixed

• fixes [Enhancement] XAML navigation inside a ListView ItemTemplate uses parent BindingContext instead of that of the ListView item #2232

API Changes

Adds TargetBindingContext enum. To use the legacy behavior of targeting the Page's BindingContext simply set this property. By default it will use the TargetElement.

Behavioral Changes

Navigation XAML Extensions & Dialog XAML Extension now correctly set the BindingContext of the Command / Extension to the Target Element's Binding Context instead of the Page's Binding Context. This correctly supports uses within Lists.

PR Checklist

• Has tests (if omitted, state reason in description)
• Rebased on top of master at time of PR
• Changes adhere to coding standard