All rules are currently disabled, except for one that I enabled for
src/Http via a new ".editorconfig" file I added there.

Other changes:

* Allow editorconfigs in MVC and Razor to flow to the root
* Consolidate a few editorconfig settings
* Tweak Ruleset config in Azure/AzureAD where it clashed.

Addresses the beginning of #9620, but it's a fair chunk of work to
enable most rules through the whole repo. That can be done directory by
directory and rule by rule by dropping .editorconfig files though.