Preserve bound actions during detach triggers

[wieslawsoltes]

Summary

• execute visual/logical detach callbacks before releasing behavior and action logical scope
• keep bound detach-trigger commands valid during the callback
• guarantee scope cleanup with try/finally, even when a custom callback throws
• add the exact compiled-XAML TabControl regression and document detach semantics

Root cause

The recent synchronous action-logical-tree cleanup exposed an ordering problem in StyledElementBehavior:

1. DetachedFromVisualTreeEventHandler detached the behavior/action logical tree
2. command bindings and inherited data context were released
3. DetachedFromVisualTreeTrigger.OnDetachedFromVisualTree executed its actions

The trigger itself still fired, but InvokeCommandAction.Command was already null. This made the reported bound method/command appear not to run when switching tabs.

The logical-tree detach path had the same ordering contract and is corrected alongside the visual path.

Changes

• notify OnDetachedFromVisualTree before DetachBehaviorFromLogicalTree
• notify OnDetachedFromLogicalTree before releasing the same scope
• use try/finally so parent, templated-parent, action lifecycle, and command observer cleanup still run if a consumer callback throws
• document that detach triggers retain their binding scope through callback execution

Tests

Reported regression

A compiled-XAML headless fixture mirrors the issue:

• a TabControl hosts a TextBlock
• the text block has DetachedFromVisualTreeTrigger
• InvokeCommandAction.Command is compiled-bound from the window data context
• switching tabs executes the bound command exactly once

The regression test fails on current master and passes with this change.

Cleanup safeguard

A behavior whose visual-detach callback throws verifies that logical parent and templated parent are still cleared.

Validation

• focused detach/action-lifetime tests: 17 passed
• focused behavior cleanup tests: 2 passed
• Xaml.Behaviors.Interactivity.UnitTests: 94 passed
• Xaml.Behaviors.Interactions.UnitTests: 90 passed, 2 pre-existing skipped
• git diff --check: clean

Closes #353