XmlnsDefinitonAttribute is not supported for "this" assembly

[etvorun]

Description

XmlnsDefinitonAttribute's are ignored for "this" assembly

Steps to Reproduce

1. New MAUI app.
2. Add MyLabel.cs containing following code

[assembly: XmlnsDefinition("http://consoto.com", "MyApp.Controls")]
namespace MyApp.Controls
{
    public class MyLabel : Label { }
}

3. Open MainPage.xaml.
4. Add xmlns:o="http://consoto.com" to root element.
5. Replace any of <Label ...> with <o:MyLabel ...>.
6. Build and run.
   Expected: no build errors, app runs fine, MyLabel is created (can see in in Live Visual Tree).
   Actual: "type not found http://consoto.com:MyLabel" build error

Link to public reproduction project repository

No response

Version with bug

9.0.40 SR4

Is this a regression from previous behavior?

Not sure, did not test other versions

Last version that worked well

Unknown/Other

Affected platforms

iOS, Android, Windows, macOS

Affected platform versions

No response

Did you find any workaround?

No response

Relevant log output

[similar-issues-ai]

We've found some similar issues:

• XmlnsDefinitionAttribute and CS0246 The type or namespace name could not be found #8158 , similarity score: 82%

If any of the above are duplicates, please consider closing this issue out and adding additional context in the original issue.

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[jaosnz-rep]

I can repro this issue on 17.14 p1.1 with MAUI 9.0.40 and 9.0.14 and 8.0.3