Add formatting guidelines with PR validation

[bart-degreed]

The goal is to define a coding style for this repository, reformat all existing code in this repository and add style validation that runs during PR build.

Steps:

• Add configuration for Resharper/Rider formatting engine
• Add JetBrains free cmdline runners (to use for local development and cibuild)
• Two-phase verification: run InspectCode to flag rule violations, then run CleanupCode and verify it does not add changes

Note this does not include writing up a document that details exactly how code should be formatted. That is a lot of work and error prone. Instead, we'll let the engine decide and reconfigure it when needed. It usually provides good feedback on what needs to change.

[bart-degreed]

Should consider to enable nullable reference types in the codebase, as part of this effort.