RTL doesn't switch the margin

Description

switch from LTR to RTL doesn't mirror the margin

Steps to Reproduce

1. add the below XAML to a content page and check the result `

    <Label Text="LeftToRight"
           Margin="10" />
    <Grid FlowDirection="LeftToRight">
        <BoxView Margin="50,0,0,0"
                 WidthRequest="100"
                 HeightRequest="100"
                 Color="Red"
                 HorizontalOptions="Start"
                 VerticalOptions="Start"
                 FlowDirection="LeftToRight" />
    </Grid>
    <Label Text="RightToLeft"
           Margin="10" />
    <Grid FlowDirection="RightToLeft">
        <BoxView Margin="50,0,0,0"
                 WidthRequest="100"
                 HeightRequest="100"
                 Color="Red"
                 HorizontalOptions="Start"
                 VerticalOptions="Start"
                 FlowDirection="RightToLeft" />
    </Grid>
   

   `

Expected Behavior

switching from LTR to RTL Should mirror the margin

Actual Behavior

switching from LTR to RTL doesn't mirror the margin

Basic Information

• Platform Target Frameworks:

  • iOS:
  • Android:
  • UWP:

• Nuget Packages: xamarin forms 3

Screenshots

current state

desired state

Reproduction Link

RTLMarginIssue.zip