Account for dual compatibility in AssetTargetFallback calculation - fix LockFileBuilderCache conflicts

[nkolev92]

Bug

Fixes: NuGet/Home#13326

Description

During solution restore, all projects share a LockFileBuilderCache. The selection criteria cache (_criteriaSets) is keyed by CriteriaKey, which compares AssetTargetFallbackFramework instances using Equals/GetHashCode.

The problem: AssetTargetFallbackFramework.Equals/GetHashCode only compared base framework properties and the fallback list. It did not account for the RootFramework being a DualCompatibilityFramework (used by C++/CLI projects to add native as a secondary framework).

This meant ATF(DCF(net6.0-windows7.0, native), [net461]) and ATF(net6.0-windows7.0, [net461]) hashed and compared as equal. When the managed project restored first, its criteria (without native) got cached, and the C++/CLI project reused those wrong criteria — so build/native/ targets were never matched.

Fix: Include DualCompatibilityFramework's secondary framework in AssetTargetFallbackFramework.GetHashCode() and Equals(), so the two produce distinct cache keys.

PR Checklist

• Meaningful title, helpful description and a linked NuGet/Home issue
• Added tests
• Link to an issue or pull request to update docs if this PR changes settings, environment variables, new feature, etc.