Enable implicit usings

[MikeAlhayek]

No description provided.

[github-actions]

This pull request has merge conflicts. Please resolve those before requesting a review.

[sebastienros]

This should not incur merge conflicts in PRs if we are lucky

[MikeAlhayek]

@sebastienros Yes. If there is, it should be easy conflict.

If you are good with this PR, please merge or approve.

[sebastienros]

I did, but GH failed. I hist approve with comment, and it only wrote the comment. Because there are too many files in the page.

[sebastienros]

Wait for another approval though, maybe someone has other things to say

[github-actions]

This pull request has merge conflicts. Please resolve those before requesting a review.

[Piedone]

Since it's impossible to review this on GitHub, and tedious in a Git client, please confirm that these are the only changes:

• <ImplicitUsings>enable</ImplicitUsings>
• Removing a bunch of namespace imports.
• The clean-up from 2176b76

If yes, then OK to merge by me after fixing the conflict.

I fixed some formatting in the latter FYI, since commenting them wouldn't even work due to the size of the diff.

[MikeAlhayek]

Since it's impossible to review this on GitHub, and tedious in a Git client, please confirm that these are the only changes:

* `<ImplicitUsings>enable</ImplicitUsings>`

* Removing a bunch of namespace imports.

* The clean-up from [2176b76](https://github.com/OrchardCMS/OrchardCore/commit/2176b7606c5598cef729d0d2e3c52107b3af3aa3)

If yes, then OK to merge by me after fixing the conflict.

That is correct @Piedone . I'll merge this after the build passes.