Use .editorconfig instead of ruleset files

We should go all in on `.editorconfig` files with analyzer settings instead of using the old ruleset files.

Start by locating the repository's old ruleset files and existing .editorconfig files, then compare which analyzer settings each contains. Done should mean the relevant ruleset configuration has been migrated to .editorconfig and the project's validation still passes, but the issue does not identify specific files or tests.

Written by the indexing model from the issue text.