[SDK-414]Feature/extract webview logic

[HarrisonHough]

SDK-414

Description

• moved all data types and classes that can be used universally for any iFrame or integration (including webGL builds)
• this is linked to this PR for WebView [SDK-414] feat: extract shared functionality rpm-unity-sdk-webview#21

How to Test

• import this branch in a fresh project or checking out Unity SDK
• NOTE: to prevent errors you will also need to checkout/import the feature branch for webview that also includes these changes feature/extract-shared-functionality
• also test the Core WebGL example as that uses some of these classes

Checklist

• Tests written or updated for the changes.
• Documentation is updated.
• Changelog is updated.