Ensure type/method refs use target module's core library

[Bertk]

Replaced direct ImportReference calls with new helpers ImportToCoreLibrary and ImportMethodToCoreLibrary to guarantee that all type and method references are correctly scoped to the instrumented module's core library (e.g., mscorlib or System.Private.CoreLib). This prevents incorrect references to System.Runtime from the coverlet assembly and improves compatibility and correctness across different .NET runtimes. All relevant field, parameter, variable, and exception handler type references are now properly redirected.

#1818

[Bertk]

Summary of the Fix

The fix uses a conditional approach:

1. IsNetFrameworkTarget(module) - Checks if module.TypeSystem.CoreLibrary.Name == "mscorlib" which indicates a .NET Framework target.
2. For .NET Framework targets (IsNetFrameworkTarget returns true):
   • Redirects type scopes from System.Runtime to mscorlib
   • This fixes the FileNotFoundException: Could not load file or assembly 'System.Runtime, Version=8.0.0.0' issue
3. For .NET Core/.NET 5+ targets (IsNetFrameworkTarget returns false):
   • Just calls module.ImportReference(type) and returns the result unchanged
   • This preserves the original working behavior
   Please run the integration tests again after rebuilding and repacking. The tests should:
   • ✅ Pass for .NET Core targets - original behavior preserved
   • ✅ Pass for .NET Framework targets - scope redirected to mscorlib (you'll need a .NET Framework test to verify this)

[Copilot]

Pull request overview

This PR adjusts how Instrumenter imports type and method references when injecting the ModuleTrackerTemplate into an instrumented module, aiming to ensure references are scoped to the target module’s core library (not the coverlet assembly’s).

Changes:

• Replaced several module.ImportReference(...) calls with new helper methods intended to redirect scopes to the target module’s core library for .NET Framework targets.
• Added IsNetFrameworkTarget, ImportToCoreLibrary, and ImportMethodToCoreLibrary helpers to centralize the redirection logic.
• Applied the helpers to imported field types, parameter/variable types, instruction operands, and exception handler catch types during tracker injection.