Add ApplicationHandler

[mattleibow]

Description of Change

This PR adds an ApplicationHandler so that an app can invoke a "quit" action. Previously this was on IPlatformServices, but now we got handlers - and not only that, it is easily overridable by setting the method in the mappers.

#1965

Additions made

• Adds ApplicationHandler
• Removes IPlatformServices.QuitApplication()
• Removes ScopedMauiContext and IScopedMauiContext
• Removes a few properties on IMauiContext and puts it inside a "proxy" IServiceProvider
• Added a MakeScoped with various overloads to wrap a context and add additional specific values (window, animation manager, fragment manager)

interface IApplication {
  void RequestTerminate();
}

class ApplicationHandler {
  CommandMapper = {
    ["Terminate"] = MapTerminate,
  }
}

It also removes the various Forms.Init() calls that do not take a maui context. This is no longer needed since we got the compat extensions using the lifecycle events.

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)
• Targets a single property for a single control (or intertwined few properties)
• Adds the property to the appropriate interface
• Avoids any changes not essential to the handler property
• Adds the mapping to the PropertyMapper in the handler
• Adds the mapping method to the Android, iOS, and Standard aspects of the handler
• Implements the actual property updates (usually in extension methods in the Platform section of Core)
• Tags ported renderer methods with [PortHandler]
• Adds an example of the property to the sample project (MainPage)
• Adds the property to the stub class
• Implements basic property tests in DeviceTests

Does this PR touch anything that might affect accessibility?

• Does this PR introduce a new control? (If yes, add an example using SemanticProperties to the SemanticsPage)
• APIs that modify focusability?
• APIs that modify any text property on a control?
• Does this PR modify view nesting or view arrangement in anyway?
• Is there the smallest possibility that your PR will change accessibility?
• I'm not sure, please help me

If any of the above checkboxes apply to your PR, then the PR will need to provide testing to demonstrate that accessibility still works.

[mattleibow]

FYI me: https://github.com/microsoft/WindowsAppSDK/issues/1479

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[PureWeen]

• I'd recommended making IMauiApplicationContext, IMauiWindowContext, and the related concrete classes internal. I could see these eventually becoming apart of our better scoping solution. For now we could expose Application/Window to users via extension methods?

• And then we can create a tracking issue for the possible exit options on Android?

[mattleibow]

Need to re-verify iOS, but I think the code is ready again.

And of course some rando errors.

[mattleibow]

Android (and others) quitting stuff: #2814

fixed things