Add CSharp Formatting

[fadi-george]

Description

One Line Summary

• formats existing c# files and add c# formatting checks

Details

• adds vscode settings to suggest using csharper extension
• adds c# formatting checker and recommended extensions
• also adds a simple ci workflow to check for formatting issues for c# files

Motivation

• want to have consistent formatting between devs

Manual Test

I ran dotnet tool install -g csharpier and then csharpier format . to format existing files.

I also modified a c# file with improper formatting and then ran format without saving.
Followed by csharpier format . to validate against formatting issues.

See previous action with an error: https://github.com/OneSignal/OneSignal-Unity-SDK/actions/runs/18358116512/job/52295294827?pr=794

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
  • If it is hard to explain how any codes changes are related to each other then it most likely needs to be more than one PR
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
  • Simplify with less code, followed by splitting up code into well named functions and variables, followed by adding comments to the code.
• I have reviewed this PR myself, ensuring it meets each checklist item
  • WIP (Work In Progress) is ok, but explain what is still in progress and what you would like feedback on. Start the PR title with "WIP" to indicate this.

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This change is 

[jkasten2]

OneSignalExample/Packages is not our code. Can we not change the formatting and omit the folder from the csharpier check command?

[fadi-george]

OneSignalExample/Packages is not our code. Can we not change the formatting and omit the folder from the csharpier check command?

Done