fix: Log All-The-Things!

[jonpryor]

Context: unoplatform/uno.extensions#3008
Context: unoplatform/uno.extensions#3011

dotnet new unoapp templates have two patterns for ILogger configuration:

1. The recommended pattern, which uses Dependency Injection (DI) via .UseLogging():

   dotnet new unoapp -preset "recommended"
   

2. The "No Dependency Injection" (NoDI) pattern, which doesn't use Dependency Injection, and instead has an App.InitializeLogging() method called from Main():

   dotnet new unoapp -di False
   

The wonderful thing is, those log different, non-overlapping, things.

The Dependency Injection pattern provides an ILogger instance to constructors of types registered with e.g.
services.AddSingleton():

services.AddSingleton<IMyService, MyService>()
// …
interface IMyService;
class MyService : IMyService {
  public MyService(ILogger<MyService> logger) => …;
}

The "No Dependency Injection" pattern provides ILogger instances from the Log<T>(T) extension method, which is used extensively within Uno itself, e.g.

// https://github.com/unoplatform/uno/blob/77c6ca0533a63be48c6bbdd830c8653e17a9b0fa/src/Uno.UI.Dispatching/Native/NativeDispatcher.cs#L146
dispatcher.Log().Error("NativeDispatcher unhandled exception", exception);

Using only DI logging initialization will miss NoDI messages.

Using only NoDI logging initialization will miss DI messages.

In order to capture all ILogger-originated messages, both DI and NoDI log initialization patterns must be used, which was not done by any dotnet new unoapp templates before this change.

Additionally, DI-based logging is optional -- it can be disabled via dotnet new unoapp -di False … -- and thus its presence cannot necessarily be relied upon.

unoplatform/uno.extensions#3011 updates HostBuilder.Build() so that if App.InitializeLogging() registers an ILoggerFactory, that instance will be used by default by DI-based logging, even if .UseLogging() is not used.

Update uno.templates to finish the harmonization:

1. Always emit an App.InitializeLogging() method, and call it from Main().`

2. Refactor App.InitializeLogging() and the .UseLogging() callback so that both call a new App.ConfigureLogging() method. ConfigureLogging() is responsible for configuringn the ILoggingBuilder instance, and this setup allows both App.InitializeLogging() and .UseLogging() to share the same code, centralizing ILogger configuration.

This should work even without unoplatform/uno.extensions#3011, ensuring that all ILogger-originated messages are logged, so long as DI-based logging is used. (This adds NoDI logging to the DI template.)

That said, it is preferred that unoplatform/uno.extensions#3011 exist first, so that even if .UseLogging() isn't used, DI-based logging will still generate log messages.

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[nickrandolph]

I think keeping the original (single) InitializeLogging method will be simpler and will be consistent across both blank and recommended templates.
In fact, we could even move this to App.logging.cs or similar in order to make it clearer that's where logging is configured.

[MartinZikmund]

Analogous change is also needed in src/Uno.Templates/content/unoapp/MyExtensionsApp.1/Platforms/Android/Main.Android.cs