Revert adding Sentry to global usings

[jhartmann123]

The latest Release 3.14.0 comes with the following feature:

Add Sentry to global usings when ImplicitUsings is enabled (true) (#1398)

We do have implicit usings enabled, with the intention was that only the often used "standard"-namespaces are added there.
Sentry on the other hand is a namespace which we use exactly once in our ASP.NET Core API projects: when configuring Sentry on startup.

For me as an "end user" of this library it does make absolutely no sense to have Sentry in the global usings.

Main issue:
The main conflict here is Sentry.User. I guess a User is not a really uncommon name for a class. Now, with the latest update we have a lot of ambiguous references between Sentry.User and our Domain-User. As a workaround I'd have to explicitly reference our Domain-User in a ton of classes over multiple projects. Which I really don't want to do.

So I vote for removing Sentry from global usings again.

[bruno-garcia]

User is definitely high chance of conflict. I suggest we take a pragmatic approach:

1. asap: release a patch release with a opt-out for ImplicitUsings (e.g: <SentryImplicitUsings>false)
2. Add to the release notes and a troubleshooting page entry to the docs on how to opt out
3. Rename Sentry.User to SentryUser on the next major change. Do such renames on other types that are high risk of conflict

[davidroth]

IMO adding Sentry to global usings was a mistake. This library is used only in the composition root in 99% of the cases. The potential for real naming clashes (User) and similar types (i.e. Sentry.Span vs System.Span<T>) is real and not worth it IMO.

[SimonCropp]

wouldnt this suffice as a opt-out ?

 <ItemGroup>
    <Using Remove="Sentry" />

[bruno-garcia]

Good tip, TIL. Worth adding to: https://docs.sentry.io/platforms/dotnet/troubleshooting/#implicit-usings

[bruno-garcia]

We discussed and agreed to revert this feature, until we release 4.0 that will include renaming some types prone to conflict.
Lets spin off a new issue to track the class renames and adding this feature back in.