.NET MAUI 9 SR5: CSS support for Border

[davidbritch]

Basic support for CSS properties that work on Border:

.myNicePurpleBorder
{
   border-color: #512BD4; /* Also supports linear-gradient, radial-gradient, named colors etc. */
   border-radius: 10; /* Always maps to RoundRectangle [Radius] internally */
   border-width: 4;
}

More info: dotnet/maui#27529

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Associated WorkItem - 406716