Deprecate UWP for v6

[jamescrosswell]

Description

As of October 2021, Microsoft officially deprecated UWP

For version 6, we'll be deprecating UWP in the Sentry SDK for .NET.

I think this is mostly about updating the Sentry docs.

There are a couple of comments in the code that we might want to update as well:

sentry-dotnet/src/Sentry/Integrations/WinUIUnhandledExceptionIntegration.cs

Lines 26 to 30 in a421af5

	// This integration is for WinUI 3. It does NOT work for UWP (WinUI 2).
	// For UWP, the calling application will need to hook the event handler.
	// See https://docs.sentry.io/platforms/dotnet/guides/uwp/
	// (We can't do it automatically without a separate UWP class library,
	// due to a security exception when attempting to attach the event dynamically.)

sentry-dotnet/src/Sentry/Internal/ProcessInfo.cs

Lines 152 to 154 in 7885354

	// GetWindowThreadProcessId is only available in the Windows SDK, so trying to call this from UWP apps will fail.
	// We wrap use of this in a try/catch as a workaround. However, we need `ExactSpelling = true` here to suppress
	// warnings about the use of this API when compiling UWP applications.

sentry-dotnet/src/Sentry/SentryOptions.cs

Line 1824 in eadf5f2

"WinRT", // WinRT, UWP, WinUI

[linear]

NET-440 Deprecate UWP for v6 (Docs)

[Flash0ver]

We also need to deprecate/remove references from Sentry, like onboarding, links to docs, and such.
E.g.

• fix(onboarding): Add dotnet-uwp to desktop category sentry#101661