Enforced diagnostics

[BarryNorfolk]

About the PR

Adds .editorconfigs to try and catch code style/general improvements to code conformity to help maintainers and contributors.

Technical details

A few things I've already ignored since we use them a hell of a lot around RT/Upstream code, like no braces on if statements, but other ones I think are still valid to enforce (Like using return values).

I'd like to get two things sorted first though:

1. IDE warnings are not build blockers, I'd like to explore if I can make that happen, if not I can make a dotnet format --verify-no-changes **/_DVA/**/*.cs task to validate output.
2. I'd like to get rid of the IDE1006 error on namespace Content.{Shared,Server,Client}._DVA where the underscore in front of _DVA is treated as an error and "unexpected". I think this might come from upstreams' .editorconfig but need to track it down.

Licensing

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