[ME][2/7] Share import transactions and simplify persistence

[tomTom1010EEE]

Description

• Share character/Studio Texture2D and Cubemap import transactions, including snapshots and failure cleanup.
• Split persistence and restoration methods into smaller, focused steps.
• Preserve public APIs, save formats and material application order.

Motivation and Context

Second stage of the maintenance split from #404, following the merged #405. This PR contains only the transaction and persistence changes.

How Has This Been Tested?

All seven targets rebuilt successfully on the merged upstream base. Existing warnings remain. The resulting source tree matches the original second-stage snapshot; later full-series KKS acceptance is not claimed as standalone runtime testing of this stage.

Screenshots (if appropriate):

No visual changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Earlier incremental review: tomTom1010-IEE#2

[starstormhun]

It's basically a lot of taking code from one place and creating separate classes for it with obscure names.