Fix StaticResourceExtension will not find the resources of the ResourceDictionary of the sibling node

[lindexi]

Fixes #6627

Description

We should call FindResourceInEnviroment when the PrefetchedValue is the DependencyProperty.UnsetValue.

wpf/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/StaticResourceExtension.cs

Lines 176 to 206 in 71944cc

	private object TryProvideValueImpl(IServiceProvider serviceProvider, bool allowDeferredReference, bool mustReturnDeferredResourceReference)
	{
	// Get prefetchedValue
	DeferredResourceReference prefetchedValue = PrefetchedValue;
	object value;
	if (prefetchedValue == null)
	{
	// Do a normal look up.
	value = FindResourceInEnviroment(serviceProvider, allowDeferredReference, mustReturnDeferredResourceReference);
	}
	else
	{
	// If we have a Deferred Value, first check the current parse stack for a better (nearer)
	// value. This happens when this is a parse of deferred content and there is another
	// Resource Dictionary availible above this, yet still part of this deferred content.
	// This searches up to the outer most enclosing resource dictionary.
	value = FindResourceInDeferredContent(serviceProvider, allowDeferredReference, mustReturnDeferredResourceReference);
	// If we didn't find a new value in this part of deferred content
	// then use the existing prefetchedValue (DeferredResourceReference)
	if (value == DependencyProperty.UnsetValue)
	{
	value = allowDeferredReference
	? prefetchedValue
	: prefetchedValue.GetValue(BaseValueSourceInternal.Unknown);
	}
	}
	return value;
	}

Customer Impact

We can use this feature to reduce duplicate creation of resources.

Regression

None.

Testing

CI and my demo: https://github.com/lindexi/lindexi_gd/tree/cd70c10df4f57fdedd9d2fbee018290e432422cf/GeacejalcurnawLarjearemwhear

And I cherry-pick the commit to build the test version in dotnet-campus/DotNetCampus.CustomWpf#9

Risk

Changed the resource lookup behavior

Microsoft Reviewers: Open in CodeFlow