Instead of simply wiping all control themes and styles that are applied to a control, we can now just remove the `ValueFrame`s which relate to the control theme that was changed.
To do this, added `ValueFrame.FramePriority` which encodes both the `BindingPriority` and source of the frame (style, control theme, templated parent control theme).
- Removes the `IStyler` service and the `Styler` implementation
- Moves the logic for applying styles and control themes into `StyledElement`
- Removes the style `TryAttach` method from the public API
- Removes style caching for now - this will need to be added back
Previously, the `IsActive` property caused the activator state to be re-evaluated, which meant that when the _debugger_ read it, it was re-evaluated, making debugging difficult.
- Always evaluate the active state from current information, don't rely on subscriptions to fire as the current state may not be up-to-date
- Don't notify the `IStyleActivatorSink` of a change immediately on subscription
Previously the combinator state was lost when traversing nested selectors. To fix it, instead of running the parent selector in `NestingSelector.Evaluate`, return the parent selector with `MovePrevious`. This required `MovePrevious` to be aware of parent styles and because I had to change its signature, I also made it internal as it doesn't need to be a public API.
Exposed by the previous fix for #8372: re-entrancy in `PropertySetterInstance.Dispose()` is causing detaching a style to call `ClearValue` on the property. Previously this wasn't a problem as `ClearValue` didn't work, but now it is.
(Also added one passing test which tests the same scenario in `PropertySetterBindingInstance` for future coverage)
Tom Edwards
José Pedro
Max Katz
Steven Kirk
Giuseppe Lippolis
Benedikt Stebner
Dariusz Komosinski