[All themes] Add Label styling

[apman]

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‼️ Do not merge yet ‼️

Needs to be coordinated with removing some RDM Label style rules

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• functionality to automatically disable the label when the parent container or the linked control (through Target property) are disabled
• added TextBlock#Colon to the template that can be addressed in consumer's style rules to enable automatically displaying a colon after all labels or labels in specific contexts, e.g.:

<Style
    Selector="Label /template/ TextBlock#Colon">
    <Setter Property="IsVisible" Value="True" />
  </Style>
</Styles>