Fix unsafe accessor generic type args

[YoelDruxman]

Fix unsafe accessor generic type args

Description

Fixes incorrect UnsafeAccessor code generation when multiple types inherit from different instantiations of the same generic base class.

Problem

When mapping types like:

class A<T> { protected T _value { get; set; } }
class A1 : A<IB> { }
class A2 : A<IC> { }

The UnsafeAccessor would generate code with wrong type arguments for the second type, causing: error CS1503: Argument 1: cannot convert from 'A2' to 'A<IB>'

Root Cause

UnsafeAccessorTypeContext caches accessors by symbol.OriginalDefinition, which ignores type arguments. When processing A1 : A<IB>, it caches the accessor. When processing A2 : A<IC>, it returns the cached accessor with IB type arguments instead of IC.

Solution

Pass the actual containingType at invocation time to BuildAssignment and BuildAccess methods, instead of using the cached symbol's type arguments. This preserves accessor caching (for class generation and naming) while using correct type arguments at each invocation site.

Checklist

• The existing code style is followed
• The commit message follows our guidelines
• Performed a self-review of my code
• Hard-to-understand areas of my code are commented
• The documentation is updated (as applicable)
• Unit tests are added/updated
• Integration tests are added/updated (as applicable, especially if feature/bug depends on roslyn or framework version in use)

[YoelDruxman]

This issue is stopping me from updating from 4.2.1 to the latest version.