Bug: Setting InputScope in XAML Style Fails when Applied to Multiple Controls

[robloo]

Describe the bug

Attempting to set the same InputScope value in a XAML defined style to multiple controls will fail. For example, the following XAML markup will fail to work as expected for the second TextBox and it will have null assigned for the InputScope instead of Number.

    <Page.Resources>
        <Style TargetType="TextBox">
            <Setter Property="InputScope" Value="Number" />
        </Style>
    </Page.Resources>
    <StackPanel>
        <TextBox Text="hello world!" x:Name="textBox"/>
        <TextBox Text="hello world 2!" x:Name="textBox2"/>
    </StackPanel>

Originally discussed with @RealTommyKlein @StephenLPeters here: #3186 (comment)

This appears to only be a problem in styles. The style seems to be creating a single instance of the InputScope object and then when it attempts to apply it to multiple controls it fails -- possible because it already has a parent after setting to the first control.

Steps to reproduce the bug

See above XAML

Expected behavior

Multiple InputScope objects should be created -- one for every instance of the control. The InputScope should be set successfully when set in a style and that style is applied to multiple controls.

Version Info

NuGet package version:

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2020 Update (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

[StephenLPeters]

@MikeHillberg or @Austin-Lamb do either you know why input scope is behaving so strangely?

[StephenLPeters]

Putting it on framework, because input scope is mostly a text box property, but the bug could be in one of a handful of places.

[chrisglein]

Not sure why this isn't a shareable instance. This seems like it should be a plain old data type, not something with state.

[robloo]

This, along with the discussion in associated PR, was probably a deep issue that still needs to be understood.