[Bug] ScrollView inside SwipeView

[Denn1Ro]

Description

I use swipeview for entire screen with TopItems(Swipe direction from up to down).
Inside the swipeview there is a grid layout which has 3 section, Header, Body, Footer.
The Body section is a ScrollView.
Up until the Xamarin.Forms 4.7.0.1179 version, the swipeview events are canceled when the user swipes inside the ScrollView(Body section) and whenever tries to swipe in the Header or Footer section the swipe event are works fine.
From the version Xamarin.Forms 4.7.0.1239 and beyond, that behavior is changed.
Now the swipeview consumes ScrollView's scrolling events, so the ScrollView is disabled for the direction that is configured in swipeview(from up to down).
I think that the child(ScrollView) should has more priority to consumes these events than his parent(SwipeView) ?
If for some reason that I don't know the priority should be as it is right now, please give me some instructions on how to disable parent(SwipeView) event when the user uses the child element(ScrollView). I find the IsEnabled property of SwipeView but it doesn't help me because that disables swipe events for the entire screen. All I need is the child element should have more priority for consuming common events from his parent.
Code example:

`<SwipeView BackgroundColor="Transparent">
        <SwipeView.TopItems>
            <SwipeItems Mode="Execute" 
                        SwipeBehaviorOnInvoked="Close">
                <SwipeItem 
                        BackgroundColor="Transparent"
                        Command="{Binding SwipeCommand}"/>
            </SwipeItems>
        </SwipeView.TopItems>
        <SwipeView.Content>
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="10*"/>
                    <RowDefinition Height="60*"/>
                    <RowDefinition Height="30*"/>
                </Grid.RowDefinitions>
                <!--HEADER-->
                <Label Grid.Row="0" Text="HEADER" Padding="20" BackgroundColor="Red"/>
                <!--BODY-->
                <ScrollView Grid.Row="1" BackgroundColor="Blue">
                    <StackLayout Spacing="20" Padding="15">
                        <Label Text="Dummy Text: 1" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 2" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 3" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 4" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 5" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 6" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 7" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 8" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 9" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 10" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 11" FontSize="Medium"  Padding="30"/>
                        <Label Text="Dummy Text: 12" FontSize="Medium"  Padding="30"/>
                    </StackLayout>
                </ScrollView>
                <!--FOOTER-->
                <StackLayout Grid.Row="2" Padding="20" BackgroundColor="Red">
                    <Label Text="FOOTER"/>
                </StackLayout>
            </Grid>            
        </SwipeView.Content>
    </SwipeView>`

Steps to Reproduce

1. Create an new Xamarin Forms
2. Copy - Paste the code above inside a content page
3. Swipe from up to down direction for all three different sections(Header, Body, Footer) in Xamarin.Forms 4.7.0.1179 and the latest version in order to detect the different behavior.

Expected Behavior

The scollview should consume the swipe event with direction from up to down and cancel his parent(SwipeView).

Actual Behavior

The SwipeView as a parent element consumes the swipe event and it cancels any other common event from his children.

Basic Information

• Version with issue: Xamarin.Forms 4.7.0.1239 and above
• Last known good version: Xamarin.Forms 4.7.0.1179
• IDE: Visual Studio for Windows

[jsuarezruiz]

@Denn1Ro Thanks for the detailed description. I am working in the fix: #12819
Tested the behavior from 4.7 to 5.0 and, the behavior in the PR is slightly different but I think better. Could you review the description of the behavior and look at the attached gif of the PR and give me your feedback? Is it the behavior you would expect?

[Denn1Ro]

@jsuarezruiz your solution is just perfect! Would you create this implementation for IOS too ?
Thank you!