Removes MappingMode from LinearGradientBrush in HasRealizationContextChanged

[dipeshmsft]

Fixes #10502

Description

As described in the issue description, LinearGradientBrushes ( LGB ) caches it bounds when we use Absolute MappingMode. However, when we apply transformations to the brush, the brush does not work work as expected. This PR removes the caching of the brush, thus resolving the issue.

Customer Impact

Developers using the LGB along with MappingMode=Absolute and RelativeTransform will get the correct behavior for the brush.

Regression

No

Testing

Not yet.

Risk

• It will have a performance impact on the application using LGB with Absolute mapping mode.
• Applications using LGB will get a different behavior now.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[h3xds1nz]

@dipeshmsft I don't think I agree with this change.

Sure, it is unfortunate that it "does not work" with transformations but well, it is Absolute after all, you should be setting the bounds and not expecting adaptations to the current space with transformations. Imho just using wrong tool for the job.

[dipeshmsft]

@h3xds1nz I came across this while fixing the borders in the new Fluent styles. WinUI uses the brush in the above syntax, and gets the expected behavior. I am not sure of there mechanism though.

I will try to look for other ways for fixing the usage.

[miloush]

I don't remember much honestly and will have to look once I am back travelling, but I don't think Absolute should depend on the size of the element, which is what I think @h3xds1nz is saying but what is happening. Certainly caching shouldn't affect the output, it should only save calculations.

[codecov]

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Additional details and impacted files

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