MAUI support

[andrueastman]

Changes include:

• [Breaking] Replacing Xamarin build targets with MAUI build targets. Xamarin users can use the MAUI build targets for ios android and macos. Closes MAUI support #413
• Enable the use of building the project with .NET CLI as Support additional target frameworks such as for Xamarin, UWP, etc dotnet/sdk#491 is resolved using MAUI targets to close Add ability to build the project with dotnet CLI #227
• Removes the Microsoft.Graph.Core.XamarinAndroid.Test project as the net6.0 target is sufficient to close Can we get a .sln file that doesn't require the Xamarin SDK installed? #39
• Updates tests and test project to net6.0 target
• Updates the GraphClientFactory.Create method to allow the HttpClient to use the extra constructor that prevents handler disposal to close Passing handlers to GraphClientFactory.Create() creates a HttpClient that disposes the handlers #373
• Updates CI/CD pipelines to use dotnet CLI commands rather than msbuild

Microsoft Reviewers: Open in CodeFlow

[baywet]

Suggested change

	if (this.batchResponseMessage.Content == null || this.batchResponseMessage.Content.Headers.ContentLength == 0 )
	if (this.batchResponseMessage.Content == null || !this.batchResponseMessage.Content.Headers.Any())