- Reversed lookup order (Extension second)
- Introduced type cache

```
PERF PROGRESS:
SourceGen - Maui.Controls.Sample (262 XAML files)

1) Unchanged:
- 15640 GetTypeByMetadata calls
- 223s

2) Extensions lookup in XmlTypeXamlExtensions.GetTypeReference() second
- 6232 GetTypeByMetadata calls (~60% reduction)
- 90s                          (~60% reduction)

3) With type cache
- 203 GetTypeByMetadata calls (~97% reduction => ~99% total reduction)
- 6s                          (~93% reduction => ~97% total reduction => 37 times faster!)
```

…an 2

…d potentially breaking behavior for scenarios besides x:Array. In this case XamlC preferred System.Array over ArrayExtension for x:Array. With the typecache it made no measurable difference in performance.