[release/7.0.1xx-rc2] [msbuild] Add a public 'CompileImageAssetsDepen…

…dsOn' property. Fixes #16065. (#16112)

Add a public 'CompileImageAssetsDependsOn' property, so that MAUI can
inject tasks that
must be completed before we compile image assets:

```xml
<PropertyGroup>
	<CompileImageAssetsDependsOn>
		$(CompileImageAssetsDependsOn);
		ResizetizeCollectItems;
	</CompileImageAssetsDependsOn>
</PropertyGroup>
```

Fixes #16065.


Backport of #16089

Co-authored-by: Rolf Bjarne Kvinge <[email protected]>

msbuild/Xamarin.Shared/Xamarin.Shared.targets

@@ -792,6 +792,7 @@ Copyright (C) 2018 Microsoft. All rights reserved.
 
 	<PropertyGroup>
 		<_CompileImageAssetsDependsOn>
+			$(CompileImageAssetsDependsOn);
 			$(_CompileImageAssetsDependsOn);
 			_DetectAppManifest;
 			_DetectSdkLocations;