[Testing] Extend NativeAOT Templates tests to cover all supported platforms

[ivanpovazan]

Description of Change

This PR improves MAUI with NativeAOT test coverage by extending the Templates tests with cases for all supported platforms.

Additionally, as we reached 0 warnings for the template MAUI app and NativeAOT (via: https://github.com/dotnet/maui/pull/21050), I simplified the test cases.

NOTE: I did not remove the logic in src/TestUtils/src/Microsoft.Maui.IntegrationTests/Utilities/BuildWarningsUtilities.cs intentionally, as we might want to use it for testing builds of apps which still have trim/AOT warnings.