Fix not being able to use Icon markup extensions as the Value of a Setter

[Difegue]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

Trying to use {ui:SymbolIcon} or {ui:FontIcon} extensions as the Value of a Setter in a Style will fail:

<ui:Button>
<ui:Button.Style>
    <Style TargetType="ui:Button" BasedOn="{StaticResource {x:Type ui:Button}}">
        <!-- Flip icon on RTL language -->
        <Setter Property="Icon" Value="{ui:SymbolIcon ArrowLeft24}" />
        <Style.Triggers>
            <DataTrigger Binding="{Binding RelativeSource={RelativeSource AncestorType=local:MainWindow}, Path=FlowDirection}" Value="{x:Static FlowDirection.RightToLeft}">
                <Setter Property="Icon" Value="{ui:SymbolIcon ArrowRight24}" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</ui:Button.Style>
</ui:Button>

SymbolIconExtension is not valid for Setter.Value. The only supported MarkupExtension types are DynamicResourceExtension and BindingBase or derived types.

Issue Number: N/A

What is the new behavior?

• The extensions can be used in Setters again.

Other information

This change was brought in #1067 , but the incriminating lines don't seem to be related to the problem this PR was fixing (adding the missing constructor)

[Veritera]

@Difegue if i remember correctly this specific part was already in the class and got only moved but feel free to correct me.

[Difegue]

I don't believe that to be the case looking at the diff of the original PR, unless I've missed something 🤔

[Veritera]

I don't believe that to be the case looking at the diff of the original PR, unless I've missed something 🤔

Hm ... looks like yeah. I could swear it was already in :s

[pomianowski]

Hey @Difegue, thanks for the work you've put in